When to start engine for a charge?

DIY
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1

Victron 100Ah, 75A alternator, Balmar 618 Orion 12/12-18A, BMV 712, solar 340w
When do you decide the battery is low, time to start up the engine. Do you go by fhe SOC percentage? Thanks

2

Hello @vic008 , Yes SOC is the answer. If you have lead acid battery charge when the battery reaches 50%. If you have lithium battery charge when the SOC reaches 10%.