question

What firmware are you running in all devices - are they up to date?

In the Venus device, can you recheck that the Multiplus is selected as the SOC source under Settings → System Setup → Battery monitor?

With an external charge source (solar charger) the Multiplus will not 'reset' the SOC % to the 'SOC when bulk finished' level when the battery voltage is raised above the absorption voltage set in the Multiplus - it will only allow the SOC % keep rising above the 'SOC when bulk finished' level.

To 'reset' the SOC % to the 'SOC when bulk finished' level you need to conduct a charge cycle with the Multiplus.

And to trigger a new charge cycle (with the Multiplus) the battery voltage needs to fall below the 'Restart bulk voltage', which for a 12V system is = Vfloat - 1.3V (max 12.9V), multiply by 2 fro 24V systems and by 4 for 48V systems.

The other option to trigger a new charge cycle with the Multiplus is to simply turn the unit off and then back on.

Long term - if you run off solar regularly and the SOC % is not tracking properly (falling overtime when the battery is actually fully charged) then you need to increase the charge efficiency - I would go direct to 100% and see how it tracks after a proper synchronization. Your batteries may have also lost some capacity over time, so it might also help to lower the capacity a little.

If you want more accurate/better SOC% measurement you really need to add a BMV/smart shunt to the system.

Thanks Mark for your reply (once again you alwasy try to help :)

However, I can't understand why the SOC is being "capped" at 39, 38, 36, 34% .... going lower every day, when the voltage always reaches absorption and higher from Multiplus setting by a good margin. This didn't happen before. I had not had a correct SOC, but I had and approximation. See old SOC calculations from older period:

I always found a way to push up. But now, since some weeks, no way to make it back up. Started descending and never ever again hit the 80-ish % mark. I did not change nothing in Multiplus in September. Only Venus OS was updated.

Coincidently, I cannot find the below options / information anymore in my system. This picture is actually from a topic of yours, Mark:

Has anybody checked if the above is still visible?

EDIT: Multiplus version: 459

MPPT chargers were using latest official release at the time of the drift started.

Good thread (newbie here).

So I just installed 600ah Lithium (x3 Superpacks, 200ah each) with Multiplus 12/3000 and 340w Solar w/ Smart MPPT.

Since you guys give great advice, what’s the recommended way to do a full charge/discharge cycle, so as to prolong the life of the battery bank?

Note, I’m using a Simarine Pico display as a Battery Monitor with (1) shunt for loads, (1) shunt for batteries, (1) shunt for solar/chargers, (1) shunt for inverter. It seems to read to correct SOC on the Simarine but it’s not identical to the Multiplus, especially since I activated the MPPT charger.

Just confirmed. The problem was the Multiplus was never in Bulk stage. Once I selected Lithium, finally on next cycle it was ok again.

So, in summary, after I added more capacity to battery, the voltage never reached a level low enough - Multiplus always in Float and SOC was incorrect.