Print Friendly, PDF & Email

As the green transition begins, militaries are left weighing the benefits of a transition from internal combustion engines (ICEs) to hybrid electric vehicles (HEVs) and even battery electric vehicles (BEVs). The defence industry has already begun to promote some of these technologies and begun to showcase what is currently possible. However, the big question remains – is making the switch viable right now?

On the face of it, there are a lot of positive benefits up for grabs by militaries through a transition to HEVs and BEVs. These range from to lowering the vehicle’s thermal and acoustic signatures, helping to decrease average detection distances by being cooler and quieter, to improving the vehicle’s ‘silent watch’ capability (the ability to keep a vehicle’s core mission systems operating without running the main engine), to extended vehicle range and budgetary savings through reductions in demand for hydrocarbon fuels. However in engineering, benefits rarely come for free, and electric vehicles are no exception.

Economic factors remain a critical consideration for operating a vehicle fleet, and benefits such as fuel savings would need to be weighed against the short-term procurement and training costs, as well as the longer-term spares and maintenance costs of running such a fleet. Aside from economic factors, there are some much more immediate physical and engineering factors which need to be considered when looking at BEVs in particular.

A CG render showing AM General ‘Humvee Charge’ hybrid electric vehicle. A lower acoustic signature, exportable power, and extended range compared to ICE vehicles are a few of the potential benefits of adopting hybrid electric drive.
Credit: AM General

As such, before dealing with HEVs, we will first compare the two opposite ends of the spectrum – all-electric BEVs and conventional ICE vehicles, as this will help to highlight the strengths and weaknesses of battery technology as it exists currently.

Battery impact on payload capacity

Perhaps one of the most important figures in when making logistical considerations is payload capacity, a figure which can be derived by subtracting the vehicle’s curb weight (how much the vehicle weighs when empty) from its gross vehicle weight rating (GVWR) – the latter represents the total design weight of the vehicle which cannot be exceeded, and includes passengers, fuel, and cargo.

To use a representative example, if an ICE-powered truck (assuming a rigid body truck for the sake of simplicity) has a curb weight of 9 tonnes, and a GVWR of 30 tonnes, then the vehicle can hold a maximum of 21 tonnes of non-towed payload. However, some of this weight has to account for the fuel and the driver, along with any spare parts or necessary supplies. So if we assume a value of approximately 800 kg in fuel, along with 100 kg for the driver, and 100 kg for a spare tyre plus some supplies, we are left with a useful payload of 20 tonnes remaining for carrying cargo. Since the Lithium-ion (Li-ion) batteries commonly used for electric vehicles have vastly inferior energy density compared to hydrocarbon-based fuels (both in gravimetric and volumetric terms), a BEV truck will necessarily be significantly heavier than an internal combustion engine (ICE) vehicle of the same approximate automotive performance. This added weight quickly begins to eat into payload capacity, as we see in the rough, back-of-the-envelope calculations below.

In gravimetric terms, diesel fuel provides approximately 12,600 Wh/kg, while a lithium-ion battery (depending on the individual design) can range from around 300 to 500 Wh/kg. As such, at first glance, it would seem that a Li-ion battery pack would need to be around 25-42 times (depending on the exact battery design) heavier than the equivalent amount of energy in hydrocarbon-based fuel. However, this potential energy doesn’t quite translate perfectly into real-world usable energy, since there are efficiency losses to heat in burning hydrocarbons which need to be factored in. Using diesel as our example, this fuel has a peak efficiency of around 50% in optimal conditions. Since these conditions will not be met all the time, we will assume an average efficiency of 45%. To feed this back into our energy density calculation, we end up with an effective energy density of about 5670 Wh/kg for the sake of this thought experiment.

Assuming this ICE truck has a diesel fuel capacity of 940 litres, this would weigh 800 kg, and we will assume a representative range of 700 km at full load with this fuel capacity. This results in an effective total energy of 4,536,000 Wh required to drive a 30 tonne vehicle for 700 km, and this is the figure a BEV truck would need to aim for to match the ICE truck’s range. BEV batteries are much more efficient, with a charge/discharge efficiency of around 95% to 98%. Assuming the best-case latter figure, to translate this into an effective energy density figure for a 500 Wh/kg battery, we would get 490 Wh/kg. Thus, in order to reach the 4,536,000 Wh required to drive 700 km, a hypothetical BEV truck would need 9,257 kg worth of battery – over 11.5 times more in ‘fuel’ than the 800 kg of the ICE vehicle. This would naturally cut into the vehicle’s available payload capacity, leaving only around 10 tonnes for payload, compared to 20 tonnes on the ICE truck.

There are several options for designers looking to overcome these problems using available options. The first is sacrificing range, since this would allow weight savings on the amount of battery required. To go back to our hypothetical BEV truck example, if we were to halve the range requirement, we could halve the battery capacity, and our hypothetical all-electric truck would be able to go from carrying 10 tonnes of cargo for 700 km to carrying 14.6 tonnes for 350 km. While this is an improvement, it also limits the truck to shorter journeys. A perhaps better solution is to limit BEV logistics vehicles to serving as tractors for semi-trailers, rather than as rigid-body trucks. Since towing a load is easier in terms of energy requirements than carrying the same load directly on the platform, this would greatly help to close the performance gap between ICEs and BEVs for many typical day-to-day applications.

A Scania electric tractor with semi-trailer. Several companies including Scania and Tesla have entered the electric truck space. However, the regional-distance designs revealed thus far have all been tractors with semi-trailers. Scania has already revealed a rigid body electric truck for shorter-range urban deliveries, and is working on a regional-distance version.
Credit: Scania

Neither option is ideal. Many militaries are likely to require both rigid-body trucks for numerous applications, and a long-haul capability is desirable in wartime conditions, particularly when operating in austere environments. Limiting BEV logistics vehicles to niche roles also provides the problem of reducing fleet commonality, which would necessitate more types of spare parts, storage, and training for how to repair and maintain them.

While the added weight already poses problems for logistical vehicles, this problem only increases in magnitude when considering battery electric drive for armoured fighting vehicles (AFVs). Most such vehicles already operate very close to their GVWR, due to their armour taking up much of their theoretical payload capacity allowance. While many modern AFV designs have a built-in margin for future growth, this margin is often relatively modest, typically in the order of a few tonnes. This gives AFV designers very little room for manoeuvre when considering adapting existing vehicle designs to battery electric drive. Aside from this added weight, there is also the impact of added volume to consider.

Battery impact on volume

A further consideration are the volume requirements of batteries. Once again, they are less efficient than their hydrocarbon-based counterparts. In volumetric terms, diesel has an energy density of 10,722 Wh/L, reducing to an effective energy density of 4825 Wh/L after factoring in efficiency losses of 55%. This can be contrasted to around 750 Wh/L for Li-ion batteries used by BEVs, reducing to 735 Wh/L when factoring in efficiency losses of 2%.

To bring this back to our previous comparison, to reach the 4,536,000 Wh of energy required to drive a 30 tonne vehicle 700 km, the ICE truck requires roughly 940 litres of fuel. By contrast, to attain the same range, a BEV truck would need batteries occupying about 6,171 litres of space – over 6.5 times more. However, this comparison is not entirely fair, since there are a lot of automotive components an ICE vehicle possesses which a BEV equivalent would not need. Typically this would include the ICE engine, gearbox, clutch/torque converter, fuel tanks, drive shaft, differential, and any transfer cases. All of these components together occupy quite a large volume inside the vehicle, which can effectively be regained for battery storage space.

The space savings would be especially pronounced if the BEV uses in-hub motors, since mounting the drive motors inside the wheels would provide even greater in-board volume savings for battery storage. However, in-hub drives can expect a lower life expectancy compared to in-board motors due to their direct exposure to terrain shocks and the elements. They also represent a point of vulnerability to enemy fire, which could result in a mobility kill of the target vehicle. Added to this, in-hub motors would represent a very large increase in the unsprung mass of the vehicle, which in turn would require a more capable suspension system and shock absorbers (likely further increasing weight) to compensate for the added upward inertial force of heavier wheels, and is likely to result in overall worse handling characteristics. The effect would be especially pronounced when travelling over rough terrain.

General Dynamics Land Systems’ Advanced Ground Mobility Vehicle on display at the Renewable Energy Rodeo and Symposium at Fort Bliss, Texas, in June 2010. The vehicle is hybrid-electric capable with in-hub electric drive. Hybrid vehicles for military purposes have been quietly under development for many years.
Credit: US Army/Stephen Baack

The added inertial load of in-hub motors would likely have additional effects when on AFVs, such as greater difficulties stabilising cameras and weapons while the vehicle is in motion, making accurate fire on the move more difficult to achieve. This could also result in incompatibility with weapon stations and turrets designed around current typical vehicle vibration limits, and may require special modifications to cope with the higher inertial loads on the wheels. As such, while in-hub drives may make it easier to find space for battery storage without adding to volume requirements, they are not necessarily the most desirable solution.

Using a conventional in-board motor to drive one set of wheels would be an alternative, but if all-wheel drive is a requirement, in typical BEV designs the various axles need their own motors powering them, with their own transmissions. This in turn would cut into space that could have been used for battery storage, meaning the designer would need to find the additional space elsewhere. Having said this, electric motors can be fairly small, and most BEV transmissions are single-speed, so both can be fitted into a fairly compact package compared to their ICE equivalents. As such, the final impact of multiple motors and transmissions on internal volume would likely be relatively minimal.

In sum, while the difference between ICEs and BEVs is not quite as pronounced when dealing with volumetric energy density as it is with gravimetric energy density, this gap nonetheless has the potential to pose serious problems of its own. If the space cannot be found by just replacing ICE drive components, new space would need to be found, which would likely impact final vehicle dimensions and thus automotive performance.

Increasing vehicle dimensions is a complex prospect. Making the vehicle wider would render it unsuitable for some roads, and complicate manoeuvring in tight spaces, as well as possibly put the vehicle outside of common rail carriage limits. Making it taller would also limit access in some areas, such as roads passing under low bridges. Making it longer would be easier, but would increase the turning circle, making it harder to manoeuvre in tight spaces.

Finding some additional volume may pose less of a problem for logistical vehicles, yet it becomes a nightmare for AFVs, which already struggle with internal volume even in the best cases. Indeed, the search for ever-more internal volume has been one of the major driving forces behind why today’s AFVs are often many times larger than their Cold War equivalents. Beyond volume, the case for military BEVs looks weaker still when factoring in the real-world environmental conditions a BEV may face.

The role of temperature on battery performance

While battery efficiency is very high under optimal conditions, it varies greatly depending on the ambient temperature. Fan Yang et al noted in their June 2018 paper in Nature that the driving range of a BEV using Li-ion batteries can drop significantly under both high and low temperature conditions, as summarised in the table below:

Ambient temperature Loss of range (local driving) Loss of range (highway driving)
-18°C 57% 40%
35°C 27% 10%


As the table shows, these losses can be quite considerable, particularly in cold weather. To bring this back to our hypothetical BEV truck – if it needed to drive 700 km in cold weather conditions of -18°C, we could anticipate needing approximately 14,533 kg of battery, thus cutting further into the useful payload. The alternative would be stopping to recharge, but this would result in highly variable mission timescales in different environments. This is far from ideal for military planners.

Added to this, battery degradation over time also poses a significant problem to BEV overall efficiency. This happens as a function of both how often the battery is charged and discharged, known as ‘cycling capacity loss’, and time, known as ‘calendar capacity loss’. As noted by Yang et al, average ambient temperatures play a significant role in both, but particularly in calendar capacity loss, with greater degradation noted in hot climates compared to cooler climates:

Geographic Location
(average temperature)
Annual calendar capacity loss after the first year Annual calendar capacity loss thereafter
Alaska (-2.7°C) 4.4% 1%
Hawaii (24°C) 9.6% 2.2%


As such, the 98% efficiency figure cited earlier represents an EV’s peak performance at the start of its life, under optimal temperature conditions. The real world is rarely as forgiving. Consequently, our hypothetical BEV truck could expect a significant reduction in range in realistic conditions over time, with the speed of degradation varying by geography and climate. This would impact life cycle costs, with replacement batteries becoming necessary to maintain performance. Yang et al cite the agreed-upon maximum battery degradation limit as being 30%, and noted that according to their data, this would translate to BEV batteries requiring replacement every 5.2 years in Florida’s warm climate, and every 13.3 years in Alaska’s cold climate.

Given that most military vehicles can be expected to spend the majority of their life outdoors, in a variety of weather and temperature conditions, this is not ideal. There are engineering solutions to this problem, such as the use of heating, ventilation, and air conditioning (HVAC) systems to cool or heat the batteries to their optimal operating temperature as needed. However, these add a degree of complexity and cost, and would primarily help when the vehicles are being used, rather than when they are left parked outdoors in an inactive state.

BEVs look to remain light over the short term

Given the above problems, it would be easy to write off BEVs as un-viable for military applications entirely, but things are not so straightforward. Speaking to representatives of GM Defense at IDEX 2023 in February, ESD was told that given where battery energy density currently sits, BEVs are viable, but mainly at the lighter end of the military vehicle market. According to Jim Khoury, then Assistant Chief Engineer at General Motors, the approximate dividing line for viability currently sits at around 5,443 kg (12,000 lb) – if the vehicle is lighter than this, batteries become a viable option, while if the vehicle is heavier, hydrogen or hybrid electric propulsion are the more viable options.

Khoury also noted that battery energy density has tended to increase every 2-3 years, and said that he estimated battery energy density would double within 10 years. According to Khoury, one effect of this doubling, is that it will raise the dividing line at which BEVs become viable, from their current level, to approximately 7,257 kg (16,000 lb). This latter figure is a large increase in relative terms, yet in absolute terms it remains far shy of the kinds of weights needed for implementing battery electric drive on medium-weight armoured vehicles, which normally range from 15-40 tonnes, let alone heavier vehicles such as main battle tanks, which are typically over 45 tonnes at the lighter end. As such, it would appear that the prospects for heavier BEV AFVs remain very limited over the medium term.

When ESD spoke to Jensen Chew, Product Director for Powertrain Electrification at ST Engineering, he agreed that this divide was likely to remain, with BEV technology used for generally lighter vehicles, and HEV for heavier vehicles, albeit only for the near-term future. Jensen stated that over the longer term, we will start to see full electric drive used for various vehicles ranging from light to heavy, wheeled and tracked. Jensen foresees this coming as a result of both continued research and proliferation of electric vehicle technology globally, and as the result of simultaneous scaling down of R&D of ICE engines.

Shown here is the GM Defense concept BEV known as the electric Infantry Squad Vehicle (eISV), which weighs just under 2,232 kg. For at least the next decade, BEVs are likely to remain on the lighter side. However, advances in battery technology are expected to gradually permit heavier designs to become viable.
Credit: GM Defense

Here Jensen touches upon an often-neglected point – that ICE engines will require continued development to match evolving efficiency requirements and emissions standards. As the investment funding and research efforts drift increasingly toward BEV technology, there is likely to come a point where ICE engine development effectively halts at large scales, giving BEV technology a greater chance to catch up and even overtake.

For the time being, however, there appears to be consensus in industry that current with current battery energy densities, hybrid drive currently represents a more viable approach to the heavier end of the AFV segment. Since HEVs primarily rely on their ICE to provide most of their power, their dependence on batteries is far lower. As such, HEVs comparatively have to sacrifice a much lower portion of their payload capacity and internal volume than BEVs. At the same time, HEVs can make use of their batteries to supply power when needed, providing a ‘silent watch’ capability, and allowing the vehicle to switch to electric drive when a lower acoustic signature is required. These characteristics lend themselves to military applications much more easily than current BEVs.

However, this does not mean that HEVs will necessarily reign supreme for the long-term. While HEVs are the more viable option for heavier vehicles today, many of the advances to be made in improving HEVs, will directly improve BEV viability at the same time. Examples include advances in battery chemistry, the development of energy-dense solid-state batteries, and the development of regenerative power systems. Over time, these advances may eventually tip the scales in favour of BEVs in all weight categories.

The promise of regenerative power

To close the power density gap with ICE vehicles, there are a number of measures which BEV and HEV manufacturers are looking into, with a particularly important development in this area being regenerative power. This technology has been used in Motorsport since around 2007, most famously on Formula 1 cars since 2009 in the form of a kinetic energy recovery system (KERS). This system works by recovering energy from the vehicle’s wheels during braking, and storing it for later use, such as supplying additional power and torque to the wheels when needed. Typically this energy would be stored in a battery on F1 cars, but it’s also possible to use supercapacitors or a flywheel to achieve much the same result.

The technology began to make its way into the commercial hybrid vehicle market and public transport applications shortly after its adoption by motorsport, referred to by the generic term ‘regenerative braking’. On hybrid vehicles the benefits are clear – by harvesting some of the energy that would otherwise be wasted during the braking process, regenerative braking provides the vehicle with what is essentially free energy, and can be used to top up the battery slightly, increasing its available power and thereby improving range.

Image shows the turbine generator for the ‘Gravity’ system, with its paddle-shaped blades for catching the high-pressure fluid sprayed from the accumulators.
Credit: Mark Cazalet

Going a step beyond regenerative braking, a US company known as Gravity Driven has developed a means of recovering energy from the vehicle suspension system, simply known as ‘Gravity’. This system operates by using a series of hydraulic shock absorbers which are modified to be more akin to pistons – moving upward or downward to pump fluid at pressure via the top and bottom of the cylinder. The cylinder is combined with fluid tubes and valves to create a closed-loop circulation system for fluid under high pressure.

Whenever the vehicle’s wheels move up in response to vehicle tilting, unevenness in the terrain, or back down from the return force of the vehicle suspension, their movement drives the piston along with them. The up and down action of the piston forces some of the fluid into one of two fluid accumulators. Once these accumulators have reached a predetermined pressure level, they discharge the pressurised fluid, spraying it onto the paddles of a turbine generator, which is rotated by this force, producing energy, thereby recharging the vehicle. The manufacturer has claimed that this system is capable of increasing an electric vehicle’s range by as much as 40%.

It should be noted that unlike the fairly common hydro-pneumatic suspension, the ‘Gravity’ system itself does not use a pneumatic component, as it is intended to complement the host vehicle’s suspension rather than replacing it outright. Therefore the vehicle’s existing suspension (whether based on hydro-pneumatics or a mechanical spring) would provide the return force to lower the wheels to their original position.

An advantage of this system over regenerative braking is that the system does not require the vehicle to brake, and thus can be done during while travelling at a fairly constant speed. However, one side-effect of this setup is that the frequency at which the system can recharge the vehicle is inherently tied to the degree of travel of the suspension, since it is this motion which charges the fluid accumulators. This means that in theory the ‘Gravity’ system should function even more effectively when travelling over rough terrain than on smooth roads, since in the former case, the suspension would experience comparatively more travel per unit of distance traversed.

The ‘Gravity’ system integrated with a ‘Humvee Charge’ was displayed at AUSA 2023. Note that in this setup, the system’s piton has been mounted within the vehicle’s coil spring suspension, with the latter providing return force to move the piston back down.
Credit: Mark Cazalet

On the subject of regenerative power systems, ST Engineering’s Jensen noted, “regenerative power recovery technologies to close the gap between all-electric and ICE drives is good technology. However, technologies, no matter how promising need to be industrialised for ease of manufacture as well as to be affordable. This will be the most critical stage of any new technology to ensure adoption.

Starting the transition

The ‘Gravity’ system was showcased on a HEV configuration of the ‘Humvee Charge’ developed by AM General and Qinetic, which was displayed at AUSA 2023. When ESD asked about the viability of a HEV or BEV for the US Army, an AM General representative noted that although an all-electric HMMVW may not be something the US Army is actively pursuing at the moment, such a vehicle could find an initial usage niche in the US Army National Guard, whose domestic mission profile would mean lower barriers to entry for the adoption of a HEV or BEV than the regular Army.

Indeed, here, the AM General representative touched upon an interesting point. Many of the critiques of adopting BEVs (and to a much lesser extent HEVs) into military service have centred on some of the challenges they would face on the frontlines, particularly when operating in austere conditions and exposed to enemy fire.

However, most major militaries have large vehicle fleets dedicated to non-frontline tasks many of which in practice rarely leave their home bases. Alongside National Guard or Territorial Army units, in regular service these can include airfield re-fuelling vehicles used by air forces, resupply vehicles used by navies, fire engines, mobile generators, some utility and staff vehicles, along with various types of transporters or loaders not tied to frontline units. Some of these vehicles could make good candidates for an earlier transition to hybrid or electric drive than their frontline counterparts, decreasing the fuel requirements of daily operation for armed forces.

While vehicles in the aforementioned roles may be the first tentative steps into the BEV world for militaries, it is likely that they will not be the last – with recent concept vehicles AbramsX and StrykerX both featuring a hybrid electric drive, and both conceptually intended for service on the frontlines.

The StrykerX (left) and AbramsX (right) concept vehicles unveiled by GDLS in October 2022 both featured hybrid electric drive.
Credit: GDLS

Overall, there are many good reasons to begin the transition to HEVs, not least because the power demands of modern mission systems are beginning to reach levels where traditional ICEs are having trouble keeping up, as noted by Jensen, “Whilst batteries have a lower load capacity, concurrently, the battlefield electrical loads have been increasing to the extent that traditional alternators and batteries start to have challenges in keeping up with the demand. This is where Hybrid Electric Drive vehicles have an advantage. In terms of payload, from a vehicle design perspective, it is about trade-offs and balancing between battery capacity (size) versus payload.

Addressing safety concerns

Battery safety has been another sticking point in the adoption of BEVs into military roles, particularly given that Li-ion batteries have become notorious for being liable to rapidly ignite when punctured. By contrast, the diesel fuel used by many military vehicles is very difficult to ignite naturally, typically requiring compression, which makes it relatively safe even when exposed to enemy fire. In fact, it has even been used as a form of protection on some vehicle designs, such as the BMP-3, which features a self-sealing fuel tank in front of the driver’s position, to provide additional protection in case the main armour is penetrated. However, battery safety has not stood still.

On the subject of battery safety, Jensen noted, “the current approach for the use of Li-ion batteries is with five different levels primarily to address safety. This starts with battery type & chemistry selection, followed by the level of monitoring and intervention by the Battery Management System. The preceding two would have defined battery selection and after which the focus is on the Thermal Management System of the battery which we go beyond just the traditional ethylene glycol type cooling before we look at battery containment and finally platform configuration. The last two [levels] will address battlefield threats.

Other manufacturers have likewise taken multiple precautions to ensure battery safety. Khoury stated that GM’s battery technology has been modelled to survive an 18g crash, and fire prevention measures are present both at the battery module level and at the vehicle integration level.

While it remains to be seen how effective these measures will prove their worth on a real-world battlefield, the initial signs are that manufacturers are taking the issue very seriously, and seeking to use multiple means to ensure that catastrophic battery fires – whether from thermal runaway or penetration by hostile fire – are prevented. An important, related question is how BEVs and HEVs should be repaired when damaged.

Modularity and field repairability

In most current vehicle designs shown so far, the batteries are built into the floor of the chassis, effectively forming a structural part of the vehicle. This is a good way to maximise the amount of batteries which can be fitted into the available volume, however, it is not necessarily the best approach for field repairability or the ability to rapidly ‘re-fuel’ the vehicle. In the latter scenario, smaller ‘hot-swappable’ battery packs may be a more desirable choice for BEV users, as they would allow a crew to swap out spent battery packs for fully charged ones, negating the need to spend precious minutes recharging.

A scaled-down model of GM Defense’s ‘Ultium’ solution integrated with a vehicle platform. The approach taken by GM Defense is one of a large integrated battery housing, containing 12 smaller modules for an SUV-type vehicle.
Credit: Mark Cazalet

Yet opting for a ‘hot-swappable’ battery design may come with some design trade-offs, such as a lower overall range because some volume would need to be sacrificed to make each battery module removable. It would also likely drive up production cost, as it would require a more complicated design, with the requirement that the modules are crew accessible. A further question to consider would be whether the user would prefer a smaller number of larger modules which can be hot-swapped using specialised heavy-lifting equipment at a base, which may entail a smaller volume and complexity penalty, or a larger number of smaller modules which can be hot-swapped by soldiers directly in the field, which may entail a larger volume and complexity penalty.

Choosing between maximising available power and the convenience offered by hot-swappable batteries is a difficult choice. Jensen shared his thoughts on the different use-cases for each, “In my view, hot-swap capability and high power density are just as important. This is because it is about how the users use their vehicles. As an example, if we juxtapose the manner in which a non-expeditionary force versus an expeditionary force operates, with the assumption that it is BEVs, battery hot-swap may make more sense to have vehicles on a continuous operation cycle for the former, whereas an expeditionary force may prefer integrated batteries but operating at a higher voltage for fast charging.

Adoption of one design over the other would have a direct impact on vehicle repairability and life cycle costs, with integrated battery vehicles more likely to need to be sent back to the factory for repairs to damaged battery modules, since the manufacturer would be more likely to have the tools and skills needed to remove and repair or replace the damaged integral battery pack. By contrast, hot-swappable designs would lend themselves to better repairability, since damaged modules could be easily swapped out for spares. Additionally, hot-swappable designs would allow for simpler upgrading – if a standardised battery format is used, older models could be rapidly swapped out for newer, higher-density models without the need to send the vehicle back to a factory to replace an integrated pack.

A scale model of GM Defense’s ‘Ultium’ battery module. Essentially this is an aluminium block housing 24 smaller pouch-type cells. Theoretically, such a module would be small enough to allow for hot-swap to be an option, if this were a direction the company decided to go in.
Credit: Mark Cazalet

Either way, manufacturers have an incentive to pick one approach, as a standardised design would allow for cost savings on the manufacturing side, leveraging economies of scale. As such, perhaps a compromise between the two designs is a safer approach. For instance, BEVs could use an integrated battery pack to store the majority of their power, but also have one or two small hot-swappable battery modules in case emergency power is needed in the field. This would allow for both efficient use of available volume, while also allowing a degree of field-repairability and redundancy. For instance, if the integrated battery on a BEV becomes damaged or simply runs out of charge in the field, the vehicle in question would have the option of making its way back to base under the power of hot-swap batteries borrowed from other vehicles in its platoon.

Times change

Even within the last few years, battery technology has come a long way in terms of power density and safety. One must remember that in many ways battery technology is still relatively nascent. It took decades of continuous development for ICEs to enjoy the levels of power and efficiency that they enjoy today, and similar levels of effort will no doubt need to be expended to get BEVs where militaries would like them to be.

Nonetheless, external factors such as mission system power demands, and the requirement for a silent watch capability, are already pushing militaries to look beyond traditional solutions such as auxiliary power units. Power demands are likely to increase further as directed energy weapons (DEWs) such as high-energy lasers (HELs) and high-power microwaves (HPMs) start to become adopted, along with active protection systems (APSs) and jamming systems for defending against small unmanned aerial vehicles (UAVs) and loitering munitions continuing to proliferate and increasingly becoming a standard part of a vehicle’s protective suite. Added to this, exportable power is also likely to become a greater requirement as manned-unmanned teaming (MUM-T) becomes more commonplace, with manned ground vehicles increasingly operating alongside UAVs and unmanned ground vehicles (UGVs).

BAE’s ACV C4UAS prototype, proposed for the USMC’s Advanced Reconnaissance Vehicle (ARV) programme. The vehicle is a good contemporary example of the massive growth in mission systems seen on contemporary designs, with the vehicle equipped with optoelectronic sight, 360° cameras, radars, a UAV, and what appears to be either an omnidirectional UAV jamming system or possibly a direction-finder.
Credit: BAE Systems

Additionally, as the civilian world increasingly transitions toward HEVs and BEVs, and R&D into ICEs begins to decline, military vehicles are at risk of being left behind. Many vehicle manufacturers have both civil and military product lines, and tend to seek synergy between the two where possible. As the civil sector increasingly transitions to HEVs and BEVs, manufacturers would likely incur significant costs by keeping open ICE vehicle production lines and supply chains just for militaries, which tend to make infrequent, low-volume orders, and represent a relatively small market share compared to the civil automotive sector. Such costs would in all likelihood be passed on to the customer, likely decreasing ICE affordability and increasing through-life costs over the long term.

In sum, while BEVs may not yet be ready for mass adoption by militaries in all vehicle classes, there are certainly some roles where militaries could look to make the switch, particularly with vehicles expected to serve primarily on or near domestic bases. Closer toward the frontlines, HEVs represent a good compromise between ICEs and BEVs, providing added power to run power-hungry mission systems, along with improved signature management for greater survivability, and generating overall fuel savings for the vehicle fleet, while continuing to benefit from advances in battery technology as they come.

It may be perhaps a few years too soon to herald the arrival of the lithium dawn for military vehicles, but over the next decade this is very likely to change. Yes, current BEV technology leaves a lot to be desired from a military perspective, but this is changing fairly rapidly, driven in large part by the civil automotive sector. Militaries are not immune to industrial or economic pressures, and the trends driving the rest of the world to electric vehicle adoption are not going to disappear. Sooner or later then, the electric AFV era is likely to arrive in earnest, and now is a good time to start preparing for it.

Mark Cazalet