When to recharge?

[vic008]

How does one know when needed? Victron 100A battery, Orion 12/12-18A, BMV 712 smart, Balmar 618 .
Was going by the BMV state of charge but dont have faith in its accuracy. Is their another way of knowing when to start engine than by the SoC ?

[PippaB]

The lower LFP knee starts somewhere between 3.2 and 3.0V/cell (depends on rates, whose research you believe, etc.) but certainly by the time your lowest cell reaches 3.0V it has less than 10% SOC left. Below 3.2V it has less then 20% left. So, easiest way to know when you must recharge is to monitor the lowest cell voltage and start charging somewhere between 3.0 and 3.2V.

Otherwise, for more normal operation, the SOC/voltage curve is very flat, so knowing exactly where you are is more difficult, especially under load. In that range I generally rely on the reported SOC and make my decision.