I had the same solar-synchronization problem last fall. During summer there was enough coming in to fill the batteries. Going into fall with shorter days I was surprised that the battery
voltage would go down quickly even though they were supposed to be 90% SOC.
Simple reason. I had left the Victrom BMV-600 in the default settings, besides the battery
capacity. The Victron decides the 100% full on:
- above certain voltage, plus
- below certain amps coming in
- for a given time
- Once the sun started fading in the afternoon the incoming current
kept the voltage above the decision point, and dropped the amps below the decision point - 100% sync set.
I increased the Victron's decision voltage to 14.4V and set the Outback charger
to 14.6V bulk/absorption and a very long float time, considering that with solar
I would be unlikely to over charge the batteries unless the boat is not used.