Battery % showing full when it is not

Had this exact issue with my Victron setup in the motorhome last winter. State of charge was sitting around 60-odd percent, plugged into hook-up at the site and — bam — straight to 100% on the Cerbo display. Hadn't charged at all, obviously.

Turns out the problem was that the battery monitor hadn't been properly configured for my battery bank. The "charged voltage" threshold was set too low, so it was triggering a "full" reading the moment any charge current appeared.

A few things worth checking:

• Synchronisation settings in the BMV or SmartShunt — is your charged voltage set correctly for your chemistry?
• Tail current — if this is set too high it'll think the battery's full way too early
• Battery capacity entered correctly in VictronConnect?

Also worth asking — are you running Fogstar or another lithium? Some cheaper BMS units send dodgy data over the comms line and confuse the GX device entirely. Seen it on here before.

Mine was sorted by recalibrating the SmartShunt and doing a proper full charge cycle to let it resync. Took a couple of charge/discharge cycles before the readings settled down and started behaving sensibly.

Anyone else had this with a particular battery brand or BMS combo? Curious whether it's more of a Victron config issue or something coming from the battery side. 🔋

@WonkyMender had this with my narrowboat setup too. Pretty sure it's a synchronisation issue — the Cerbo resets SOC to 100% on any detected "charged" condition, even if the battery hasn't actually hit the absorption/float cycle properly.

Worth checking a few things:

• Charge voltage tail current setting in VictronConnect — is it set correctly for your battery chemistry?
• What's your charged voltage threshold set to? If it's too low, shore power will trigger a false 100% reset
• Are you using a smart shunt or relying purely on the MPPT for SOC?

On my setup I had to dial the tail current right down and bump the charged voltage threshold up before the synchronisation behaved properly. Also noticed it was worse in cold weather — batteries weren't actually accepting a full charge but Victron didn't know that.

@WonkyMender classic Victron moment — the Cerbo thinks a full charge is whatever voltage you've told it counts as full, not what your Fogstar cells actually consider full, so if your absorption voltage is set a touch low it'll never really top off but still declare victory like it won a gold medal at the Olympics.

@WonkyMender worth checking your charged voltage and tail current settings in VictronConnect — these are the two trigger points the Cerbo uses to decide "right, that's 100%." If your tail current threshold is set too high, it'll call full charge well before the batteries actually are. I had mine set at the default 4% and it was triggering far too early on my LiFePO4s. Dropping it to around 1-2% made a massive difference. Also double-check your charge efficiency factor while you're in there — a figure that's drifted off can compound the drift over time and you'll never catch up properly between genuine full cycles.

Hey @WonkyMender, just to add to what @MistyMender is saying about those settings — once you've got the charged voltage and tail current dialled in correctly, it's also worth doing a proper full absorption cycle to let the system actually reach 100% legitimately. That gives the Cerbo a solid reference point to calibrate from. I had something similar on my setup and found the SOC kept drifting because I'd never let it complete a genuine full charge — always pulled it off hook-up too early. After one good long absorption cycle it started tracking much more accurately. Also make sure your battery capacity is set correctly in the system settings, as an incorrect Ah figure will throw the whole calculation out from the start.

@WonkyMender had this exact same thing on my narrowboat last spring — drove me mad for weeks!

One thing nobody's mentioned yet: even when you nail those settings, the Cerbo can still drift over time if you're not doing proper full cycles regularly. It basically loses track.

What sorted mine was enabling automatic synchronisation so it resets the 100% reference point when all the conditions are genuinely met together — not just voltage alone. Found that buried in the BMV settings rather than the Cerbo itself, easy to miss.

Also worth doing a manual sync once you know the bank is genuinely full (proper absorption completed, tail current hit) just to give it a clean starting point. Mine's been rock solid since. 🙌