Victron energy BMV-702 Manuel page 36

5.2.5 What to do in case of an alarm during discharging
The individual batteries or cells of a battery bank are not identical, and
when fully discharging a battery bank the voltage of some cells will start
dropping earlier than others. The midpoint alarm will therefore nearly
always trip at the end of a deep discharge.
If the midpoint alarm trips much earlier (and does not trip during charging),
some batteries or cells may have lost capacity or may have developed a
higher internal resistance than others. The battery bank may have reached
the end of service life, or one of more cells or batteries have developed a
fault:
a) In case of series-parallel connection, disconnect the midpoint parallel
connection wiring and measure the individual midpoint voltages during
discharging to isolate faulty batteries or cells.
b) Charge and then test all batteries or cells individually.
5.2.6 The Battery Balancer (see datasheet on our website)
The Battery Balancer equalizes the state of charge of two series connected
12V batteries, or of several parallel strings of series connected batteries.
When the charge voltage of a 24V battery system increases to more than
27,3V, 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 0,7A 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 48V battery bank can be balanced with three Battery Balancers.
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