Victron 200Ah lithium been sitting at 97% for days — BMS issue or just how it is?

Been having the exact same thing with my Fogstar Drift 200Ah in the van — sat at 97% for nearly a week and I couldn't figure out if something was wrong or if that's just… normal?

After a bit of digging it seems like lithium cells can be genuinely tricky to top-balance, especially if your charger isn't holding the absorption voltage long enough. A few things worth checking:

• Absorption time — is your Victron MPPT or charger set to hold at the correct voltage (typically 14.2–14.6V for LiFePO4) for long enough?
• Cell drift — could one cell be slightly out of balance, causing the BMS to cap the state of charge early?
• BMS calibration — some BMS units need a proper full cycle (charge to 100%, discharge to a low %, then recharge) to recalibrate their SoC reading

On mine it turned out the Victron SmartSolar was cutting to float too quickly, so the battery never actually finished absorbing. Bumped the absorption time up and it finally hit 100%.

That said, I've also read that some BMS firmware just reports 97% as a kind of conservative ceiling — has anyone else noticed this varies between brands?

Is yours a Victron Smart Lithium, or a third-party battery with their own BMS? Makes a difference in how much you can actually tweak. Would be curious whether anyone's had this with a Battle Born or a Chinese-branded cell like Jakiper — wondering if it's a universal lithium quirk or more BMS-specific.

@VoltVicky had exactly this with my Fogstar 200Ah on the boat last summer — sat stubbornly at 97-98% for ages and I was convinced something was off with the BMS.

Turns out lithium cells can be surprisingly slow to balance at the top end, especially if you're not regularly hitting a proper absorption charge. Is your Victron charger actually completing the absorption phase, or is it cutting out early?

Worth checking in VictronConnect — are any individual cells showing noticeably higher voltage than the others? That top-end divergence is usually what's holding it back from hitting 100%.

Did yours eventually balance out on its own, or did you have to manually trigger a full charge cycle? Curious whether the Drift's BMS handles it differently to what I've seen on mine.

Hey @VoltVicky — worth checking whether your charger is actually completing its absorption phase properly before dropping to float. If it's cutting out early, you can end up perpetually hovering just below full without the BMS ever triggering that final top-up.

Also, what's your absorption voltage set to? With LiFePO4 you want to be hitting around 14.2-14.6V and holding it there long enough for the current to tail off properly. If you're running solar and there's been patchy cloud, it might just be nibbling at the top repeatedly without ever finishing the job. Totally normal behaviour in that case — frustrating, but harmless. Your cells are likely fine! 😊

@VoltVicky this is actually pretty common with lithium and not necessarily a fault. The voltage curve on LiFePO4 is incredibly flat through the mid-range, so your BMS is essentially guessing at SOC based on voltage — and it can get "stuck" at a reading until there's enough load to recalibrate it.

What helped me was doing a proper full charge followed by a decent discharge cycle (I run mine through the EV charger which pulls a good consistent load). Forces the BMS to recalibrate its endpoints.

Also worth checking your Victron settings — if absorption time is too short it might be cutting out before truly hitting 100%, so 97% could actually be your effective full charge. Check the bulk/absorption logs in VRM if you've got it connected.

Not a fault, just LiFePO4 being awkward.

My Fogstar in the shepherd's hut did this for two weeks before I realised my Victron MPPT was bailing out of absorption early because the solar kept dipping behind clouds and resetting the timer — worth checking your absorption time settings in VictronConnect rather than assuming the BMS is haunted.