Balancing terminals in lithium battery...

[Externet]

Hi.
A tool battery has the management circuitry inside; why are the cell terminals [c1 c2 c3 c4] also brought outside to the charger ?

I understand thermal and identifier contacts to enable and select charger control; but why the string taps ?

(pictured is a DeWalt pack)

 

[Diver300]

The title of your question is the answer.

Those terminals are probably used to keep the battery pack balanced. If some cells have a higher self-discharge rate than others you can get the situation where the voltage on some cells is significantly lower than others.

That is detected by measuring each cell voltage separately. Unbalance is dealt with by discharging the cells with a higher charge, normally at a much lower rate than the main discharge. Discharging individual cells can be done by a charger.

Either measuring individual cell voltages or discharging individual cells needs low current connections to the connections between each cell.

Electric cars have typically 100 or so cells in series. Balancing is done inside the battery pack, but all 100 individual cell voltages are available to the battery management system.