A large FE lithium-ion battery cell, here compared to a much smaller early F1 KERS cell
The FE battery box contains over 150 individual lithium-ion cells, each one roughly between the size of an iPad and an A4 padded envelope and stacked upright in rows. The cell chemistry is designed specifically for the needs of each application and that’s a closely guarded secret at Williams. With all those cells connected together in series. An innovative cooling system is integrated into the battery box to help maintain stable temperatures across the entire unit.
A non-conductive fluid, known as a dielectric, is pumped around the inside of the battery case and around each cell, before being circulated through a traditional style, sidepod mounted, cooling radiator and back into the box.
With the car stationary inside the garage, powerful blowers and dry ice are used to cool the radiators and consequently the battery while it’s recharged, a process which takes around 45 minutes, but one that can only begin once the unit has been pre-conditioned, or brought into the optimum temperature window by the team.
Batteries have to be strictly maintained and their cell temperatures are carefully monitored at all times by a sophisticated battery management system (BMS), sitting inside the box on top of the cell modules. The system has the ability to shut down cells if required, or switch to a reduced power failsafe mode if things get a little too hot.
source - f1elvis