Unable to load Superpack back to 100%

Been wrestling with something similar on my van build and figured this thread was worth starting properly.

Running a bank of Fogstar Drift 100Ah cells (four of them, so 400Ah total) charged via a Victron Orion-XS from the alternator, a SmartSolar MPPT 100/30 on the roof panels, and a Multiplus-C 12/1600 for shore power when I'm on a site.

The issue I kept hitting: the bank would sit stubbornly at 96–97% according to the BMV-712, never quite kissing 100%. Spent a good few evenings down rabbit holes on the Victron Community forum before I started suspecting the absorption voltage settings weren't quite aligned across all three charge sources. Each device was doing its own thing — the MPPT finishing absorption whilst the Orion was still in bulk, that sort of overlap chaos.

What seemed to help was syncing the absorption voltage across all three to 14.2V and letting the Multiplus take the lead as master when shore power's available. The BMV started reporting full SoC much more consistently after that.

Still not 100% convinced it's sorted, mind. Some mornings it's spot on, others it drifts a few percent shy.

Curious whether anyone else running multiple charge sources into a Superpack or similar prismatic LiFePO₄ setup has had this? I wonder if it's partly a BMS tail current quirk — the cells are full but the BMS isn't signalling it cleanly to all devices simultaneously.

Anyone played with the charge current tail settings on the MPPT or Orion to tighten this up?

@WildHermit — had almost identical grief with my garden office setup last winter.

The culprit for me was the absorption voltage being set just a hair too low on the DC-DC charger. The Fogstar Drift cells are genuinely fussy about hitting that upper knee properly — they'll sit at 99% looking smug and refuse to budge.

Worth checking your charger's absorption voltage matches Fogstar's own spec sheet rather than a generic LiFePO4 profile. There's often a 0.1–0.2V discrepancy that sounds trivial but makes all the difference across a 400Ah bank.

Also — how long is your absorption phase set to run? Mine was cutting out too early before the cells had actually balanced. Extended it to 2 hours and suddenly I was seeing genuine 100% regularly.

What DC-DC charger are you actually running? That detail got cut off in your post.

Hey @WildHermit, sounds frustrating! One thing worth checking that hasn't been mentioned yet — what's your absorption voltage set to on the DC-DC charger? The Fogstar Drift cells are LiFePO4 I assume, so you want to be hitting around 14.2-14.6V per 12V battery (or scaled accordingly if you're running 24/48V). If your charger is cutting out of absorption too early due to a tail current threshold set too aggressively, you'll consistently land short of 100%.

Also worth checking whether your BMS is throttling charge current as cells near the top — sometimes what looks like a charger issue is actually the BMS doing its job a bit too enthusiastically.

What DC-DC charger are you running? Makes a big difference to what settings are actually accessible to you. Some budget units give you very little to play with.

Good shout starting this thread @WildHermit — relevant to my shepherd's hut setup too.

One thing I'd add that nobody's touched on yet: have you checked whether your DC-DC charger has a dedicated LiFePO4 profile, or whether you're running it on a generic lithium setting? On my Victron Orion-Tr Smart I initially had it defaulted to something that was cutting absorption short because the voltage curve didn't quite match Fogstar's recommended parameters.

Worth pulling up the Fogstar spec sheet and manually cross-referencing your charger's absorption voltage and time settings against what they actually recommend. The Drift cells have fairly specific requirements and a generic profile often undershoots.

Also — what's the charge current relative to your 400Ah bank? If it's too low, the charger might be timing out before cells genuinely top up.

Interesting thread — similar issue came up when I was sorting the emergency backup system for my shepherd's hut.

One thing nobody's touched on yet: have you verified your DC-DC charger's charge profile is actually set to lithium, not AGM or gel? Sounds obvious, but I've seen Victron Orion units shipped with a default profile that's completely wrong for Fogstar cells. The BMS will quietly reject the charge once voltage hits a threshold it doesn't like, and you'll just sit there scratching your head wondering why you're stuck at 94%.

Worth pulling the VictronConnect app and checking the exact absorption voltage the charger is pushing — what does yours show? And what voltage does the Fogstar BMS datasheet actually specify for that cell chemistry? Those two numbers need to be quite close before anything else makes sense to diagnose.

Worth checking your DC-DC charger's charge profile is actually set for LiFePO4 and not AGM/gel. Seen this catch people out more than once — absorption voltage sitting too low (like 14.1V instead of 14.6V) means you'll never top the cells off properly.

Also, 400Ah is a decent bank. What DC-DC are you running? Some of the cheaper units struggle to push enough current to bulk a bank that size in a reasonable time, so it looks like it's not reaching 100% when really it's just timing out before finishing the job.

My Victron Orion-Tr Smart sorted similar headaches once I got the profile dialled in via the app. Bluetooth visibility makes a massive difference for diagnosing this stuff — can you actually see your charge curve in real time?