Bank Charging - Battery Design

Bank charging is where we split the pack in two to charge it. Thus an 800V drive pack becomes two 400V packs in parallel for charging.

Porsche Macan PPE

If the station is using 400-volt technology, the all-electric Macan uses ‘bank charging’ for the first time, whereby corresponding high-voltage switches (gates) are automatically switched in the battery before the actual charging process begins. This effectively splits the 800-volt battery into two batteries with a nominal voltage of 400 volts each that can be charged in parallel on one 400-volt charging station without an additional HV booster. If necessary, the states of charge of the two battery halves are first aligned before they are charged together.

The same pack is used in the Porsche Macan EV and the Audi Q6 e-tron, both have the split pack charging.

A split pack means you essentially have two battery packs and thus: 2x BMS, 2x fuses, 2x contactors, 2x current sensors. Thus adding cost, complexity and more failure modes.

Also, splitting the pack and moving from a series connection at 800V to the two packs arranged in parallel means the two packs have to be very close in terms of overall voltage, probably <15V difference. This is achievable when the packs are new, but could become more difficult as the packs age.

Whether this is preferable to fitting a DC-DC boost converter instead is platform-dependent: bank charging avoids the converter’s conversion loss and recovers more of the charger’s power, at the cost of duplicated pack hardware, while a DC-DC converter is simpler but caps 400V charge power at whatever the converter can handle. See the 800V Architecture page for a fuller comparison of the two approaches, including how Porsche moved from the DC-DC converter on the Taycan to bank charging on the Macan.

BMS

“Bank Charging” multiplies the BMS workload. High-voltage switches physically split the 800V pack into two 400V halves that charge in parallel. This strategy drastically increases the complexity of the control system:

Component Duplication: Splitting the pack requires duplicating key electrical elements
- two separate BMS logic channels
- two main contactor assemblies
- two high-voltage fuses
- double the current sensors (four instead of two)
Voltage Alignment and Aging: Before closing the switches to charge in parallel, the BMS must ensure the open-circuit voltages of the two battery halves match closely (within 15V) to prevent dangerous circulating currents. This alignment requires complex localized balancing procedures, which become significantly more difficult to control as the two pack halves age and develop differing internal resistances over the vehicle’s lifespan.

References

Optimal balance between performance and range, Newsroom, Porsche