Victron Energy - Battery Balancer - (State-of-Charge Equaliser)

The Battery Balancer (state-of-charge equaliser) balances the state of charge of two 12 V batteries connected in series.

This balancer can also be used with several parallel strings of batteries connected in series.

If the charge voltage of a 24 V battery system rises above 27 V, the Battery Balancer switches on. It compares the voltages of the two batteries connected in series. The Battery Balancer then draws a current of up to 1 A from the battery (or the batteries connected in parallel) with the highest voltage.
The resulting difference in charging current then causes all batteries to equalise to the same state of charge.

If necessary, several balancers can be connected in parallel. A 48 V battery bank can be balanced using three Battery Balancers.