Discharge graph showing cell voltage at various depths of discharge for different discharge rates
The BMS will turn off all loads as soon as a battery cell voltage drops below the low voltage threshold.
Although a BMS is used, there are still a few possible scenarios where the battery can be damaged due to over discharge. This
can occur if small loads, such as: alarm systems, relays, standby current of certain loads, back current drain of battery chargers
or charge regulators, slowly discharge the battery when the system is not in use.
In case of any doubt about possible residual current draw, isolate the battery when the system is not in use. Do this by opening
the battery switch, by pulling the battery fuse(s) or by disconnecting the battery positive cable.
A residual discharge current is especially dangerous if the system has been discharged completely and a low cell voltage
shutdown has occurred. At 2.8V cell voltage there is approximately 3% remaining capacity and at 2.6V there is about 1%
remaining capacity.
After shutdown due to low cell voltage, a capacity reserve of 1% corresponds with 1Ah left in a 100Ah capacity battery. The
battery will be damaged if the remaining capacity reserve is drawn from the battery. A residual current of 10mA for example may
damage a 100Ah battery if the system is left in discharged state during more than 4 days (100 hours).
If all cells are 2.8V, this means that the battery terminal voltage is 11.2V (22.4V) and if all cells are 2.6V the battery terminal
voltage is 10.4V (20.8V). Be aware that the BMS will turn the loads off as soon as one cell drops below the low voltage threshold.
This might not necessarily correspond with the battery terminal voltage. So, if investigating low voltage scenarios, always use
VictronConnect to look at the actual cell voltages and do not just rely on the battery terminal voltage.
7.4. Cell under voltage pre-alarm
The battery sends a signal to the BMS in case of imminent cell under voltage. This is used by the BMS to generate a pre-alarm
signal. This signal will give an advanced warning that the BMS is about to generate a “load disconnect” signal and that the loads
are going to be turned off. This happens at a default cell voltage of 3.10V and the range is 2.80V to 3.15V.
Please note that older batteries do not support pre-alarm.
Lithium Battery Manual
Page 27
Battery charging and discharging