Victron energy BMV-712 Smart Manuel page 20

3.10 Additional functionality of the BMV-702 and -712
In addition to the comprehensive monitoring of the main battery system,
the BMV-702 and -712 have a second monitoring input. When enabled,
this secondary input has three configurable options, described below.
3.10.1 Auxiliary battery monitoring
Wiring diagram: see the quick installation guide. Fig 3
This configuration provides basic monitoring of a second battery,
displaying its voltage. This is useful for systems with a separate starter
battery.
3.10.2 Battery temperature monitoring
Wiring diagram: see the quick installation guide. Fig 4
The cable with integrated temperature sensor has to be purchased
separately (part no: ASS000100000). This temperature sensor is not
interchangeable with other Victron temperature sensors, as provided with
Multis or battery chargers. The temperature sensor must be connected to
the positive pole of the battery bank (one of the two wires of the sensor
doubles as the power supply wire).
The temperature can be displayed in degrees Celsius or degrees
Fahrenheit, see section 4.2.5, setting number 67.
The temperature measurement can also be used to adjust battery
capacity to temperature, see section 4.2.5, setting number 68.
The available battery capacity decreases with temperature.
Typically, the reduction, compared to the capacity at 20 °C, is 18 % at 0
°C and 40 % at -20 °C.
3.10.3 Midpoint voltage monitoring
Wiring diagram: see the quick installation guide. Fig 5 - 12
One bad cell or one bad battery can destroy a large, expensive battery
bank.
A short circuit or high internal leakage current in one cell for example will
result in under charge of that cell and over charge of the other cells.
Similarly, one bad battery in a 24 V or 48 V bank of several series/parallel
connected 12 V batteries can destroy the whole bank.
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 equalise charging, but large differences will result in
damage during charging due to excessive gassing of the cells or batteries
with the highest initial state of charge.
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