The service life of an expensive battery bank can be substantially shortened due to state of charge unbalance. One battery with a slightly higher internal leakage current in a 24 V or 48 V bank of several series/parallel connected batteries will cause under-charge of that battery and parallel connected batteries, and over-charge of the series connected batteries. Moreover, when cells or batteries are connected in series, they should all have the same initial state of charge. Small differences will be ironed out during absorption or equalize charging, but large differences will result in damage due to excessive gassing (caused by overcharging) of the batteries with the higher initial state of charge and sulphation (caused by undercharging) of the batteries with the lower initial state of charge.

The battery balancing
The Battery Balancer equalizes the state of charge of two series connected 12 V batteries, or of several parallel strings of series connected batteries.

When the charge voltage of a 24 V battery system increases to more than 27,3 V, the Battery Balancer will turn on and compare the voltage over the two series connected batteries. The Battery Balancer will draw a current of up to 0,7 A from the battery (or parallel connected batteries) with the highest voltage. The resulting charge current differential will ensure that all batteries will converge to the same state of charge. If needed, several balancers can be paralleled. A 48 V battery bank can be balanced with three Battery Balancers.

LED indicators
Green: on (battery voltage > 27,3 V)
Orange: lower battery leg active (deviation > 0,1 V)
Orange: upper battery leg active (deviation > 0,1 V)
Red: alarm (deviation > 0,2 V). Remains on until the deviation has reduced to less than 0,14 V, or until system voltage drops to less than
26,6 V.

Alarm relay
Normally open. Closes when the red LED switches on, and opens when the red LED switches off.

Alarm reset
Two terminals are available to connect a push button. Interconnecting the two terminals resets the relay. The reset condition will remain active until the alarm is over. Thereafter the relay will close again when an alarm occurs.

Even more insight and control with the midpoint monitoring function of the BMV-702 battery monitor
The BMV-702 measures the midpoint of a string of cells or batteries. It displays the deviation from the ideal midpoint in volts or percent. Separate deviation percentages can be set to trigger a visual/audible alarm and to close a potential free relay contact for remote alarm purposes.