Battery-swap heavy goods vehicles also require thermal management

Battery-swap heavy goods vehicles also require thermal management
At 2 am in January, at a battery-swap station. A driver, on his second night shift of the week, slowly drove his lorry into the station; the gantry crane operated automatically, and after about five minutes, the vehicle had been fitted with a fully charged battery and drove off. From the perspective of logistics efficiency, this process was nothing short of perfect. However, as the driver switched on the cab heating and watched the windscreen gradually mist up, he realised that the five-minute ‘efficient’ battery-swapping process had not resolved the predicament he faced.

Although the battery-swapping model eliminates charging wait times, it cannot eliminate the impact of temperature. We frequently emphasise this point to fleet engineers – usually during the first winter following the official launch of a battery-swapping project, once the technical specifications have been finalised.

The thermal management challenges have not disappeared; they have merely been ‘shifted’: part of the burden has been transferred to the battery-swapping stations, whilst another part remains on the lorry. It is precisely this part that remains on the lorry that is often the most easily overlooked.

The battery’s ‘second home’—the storage rack
For plug-in lorries, the battery typically remains on the vehicle and undergoes slow charging overnight. By comparison, the ‘living’ conditions for batteries in battery-swapping systems are far harsher: they undergo rapid charging at swapping stations, are fitted to lorries to complete a shift’s transport tasks, are then swapped out, and immediately enter the next round of rapid charging.

Currently, standard battery packs used in heavy goods vehicles all exceed 400 kWh in capacity, with existing designs even reaching 432 kWh and 513 kWh. Charging these high-capacity batteries at the rates required for commercial operations inevitably generates heat – and this heat ultimately becomes a problem that battery-swapping stations must address.

The same applies to low-temperature issues.

If batteries are left idle on unheated storage racks on winter nights, the charging rate slows down and the batteries age more rapidly during this process. In low-temperature environments, battery cells struggle to accept a charge; forced charging comes at the expense of the battery’s cycle life.

Consequently, battery swap stations must assume the thermal management responsibilities that would otherwise fall to the trucks themselves, namely ensuring that batteries remain within an appropriate temperature range—preheating them before the morning rush hour and cooling them during the afternoon charging peak.

This thermal management capability must be incorporated into the design of the battery-swapping stations and configured to meet peak-period demands. If designed solely for average operating conditions, by 6.00 am the station is likely to be filled with ‘frozen’ batteries, forcing vehicles to queue and wait.

Even in January, drivers must carry out their duties as usual.
The cab does not enter the storage racks along with the battery. At temperatures as low as –20 °C, drivers require heated air to keep warm and ensure a clear view through the windscreen; batteries maintained solely at the ‘swapping station ambient temperature’ are clearly unable to meet these requirements.

For battery-swap trucks, cab heating is a ‘standard’ requirement, just as it is for any other heavy-duty electric truck – that is, the vehicle’s own cooling circuit must be equipped with a high-voltage coolant heater. Take our company’s Q-series products as an example: their power output ranges from 15 to 35 kilowatts, with voltages spanning 400 to 1,100 volts.

The temperature of the battery pack is also subject to fluctuations. When the battery pack leaves the battery-swapping station, its temperature is still within the ideal range, but it will subsequently operate for extended periods in a low-temperature environment. As the temperature drops, available power decreases accordingly; therefore, the truck must be equipped with sufficient on-board heating capacity to ensure the battery pack remains within the normal operating temperature range until the next battery swap.

If vehicle configurators mistakenly assume that battery swap stations can resolve all thermal management issues, they will discover during night-time operations in January that this is not the case—we would prefer them to realise this during the planning stage, rather than waiting until actual operations to uncover the problem.

Connectors are put through their paces every single day.
For plug-in trucks, the cooling circuit is typically a closed system requiring no external connections; however, for battery-swap trucks, if the design incorporates fluid connectors, these must endure repeated plugging and unplugging every day—often in environments filled with dust and grit, at freezing temperatures, or under time pressure.

Every insertion and removal cycle causes wear to the seals, puts the performance of self-sealing valves to the test, and may allow air to enter the cooling circuit. Whilst an ‘air lock’ in the cooling circuit might occur only once every ten years in a truck with a closed cooling system, it becomes the norm in a battery-swap fleet.

Anyone responsible for planning battery-swap vehicles should adopt three practices: firstly, require suppliers to specify the insertion and removal cycle life of connectors in writing; secondly, establish dedicated coolant filling and venting procedures tailored to the operational environment of battery-swap stations (rather than repair workshops); and thirdly, incorporate coolant condition monitoring into the key performance indicators (KPIs) for battery-swap stations.

In a battery-swapping network, the reliability of thermal management depends to a large extent on standardised management at the interfaces – after all, when problems arise, people tend to attribute them to the chemical properties of the battery itself.

A five-minute battery swap leads to up to two hours of knock-on effects
Take the operational conditions in January as an example: to conserve energy, battery-swapping stations maintain battery packs at a lower temperature overnight; Consequently, when a battery pack is fitted to a lorry, its temperature is only –15°C.

At this point, although the lorry has sufficient charge, it cannot perform to its full potential: discharge power is limited, energy recovery (braking) is impeded, and rapid recharging is not possible until the battery pack has warmed to an appropriate temperature. Although the battery swap process itself takes only five minutes, the resulting performance limitations may persist for approximately two hours.

If the battery pack could be preheated using grid electricity at the battery-swapping station, this would not only be more cost-effective but would also avoid taking up the truck’s actual operational time.

Consequently, battery-swapping agreements must include ‘thermal management clauses’ that clearly specify the temperature of the battery pack at the time of handover and require the battery-swapping station operator to ensure this target is met. Early battery-swapping contracts often overlooked this point, and the cost of neglecting it can be extremely high.

Our recommendations regarding technical specifications
If a fleet operator were to submit a battery-swapping technical specification to us tomorrow, we would prioritise the review of the following five elements:

The temperature control capabilities (heating and cooling) of battery swap stations should be sufficient to meet battery swap demand during peak periods.
The temperature range at the time of battery pack handover should be clearly specified in the operating agreement.
Trucks should be equipped with an independent coolant heating system for cab heating, defrosting and maintaining the battery pack temperature; this system should operate independently of the battery swap station.
The cycle life specifications for coolant connectors (quick-release couplings) should be clearly defined, as should the operational procedures for draining and refilling coolant at battery swap stations.
Temperature data for each battery pack during every cycle should be recorded and incorporated into the fleet’s key performance indicators (KPIs) for evaluation.
Battery swapping is an effective solution to the problem of excessively long charging times, but it does not resolve temperature-related challenges. Projects that attempt to resolve temperature issues through battery swapping often find themselves having to retrofit heating systems by the second winter.

Frequently Asked Questions on this Topic
Do lorries operating under a battery-swapping model need to be equipped with lower-power on-board heaters?
No. The requirements for cab heating and defrosting remain unchanged; the vehicle still needs to be heated whilst in motion to maintain the battery pack temperature. Battery-swapping stations are solely responsible for temperature control related to charging and cannot cover the full range of thermal management functions required for winter operation.

Can the temperature control at battery-swapping stations completely replace the vehicle’s own battery heating system?
It can replace pre-departure preheating and temperature control during charging, but it cannot maintain the battery pack’s temperature in cold environments over extended periods. Both the temperature control functions at battery-swapping stations and the on-board heater are indispensable.

Who should bear the cost of the energy consumed by battery swap stations during the preheating process?
This falls within the commercial sphere, but must be clearly defined in the contract and listed alongside the relevant clauses concerning battery handover temperature. Compared to the battery cycle life that is protected and the downtime that is avoided, the energy consumption required for battery pack heating is negligible.

Are you planning to develop a battery-swap vehicle or a battery-swapping station? Please provide us with the operating conditions, environmental conditions and battery pack specifications. We will calculate the capacity required for the on-board heating system and specify the thermal management requirements for the battery-swapping station, so that these can be incorporated into the relevant agreements.