Finally sorted my battery bank after 18 months of faff — here's what changed everything

After bouncing between a tired pair of 110Ah AGMs and a secondhand 200Ah lithium that kept throwing BMS errors, I finally bit the bullet last autumn and built a proper 280Ah LifePO4 bank using Fogstar Drift cells. Four 280Ah prismatic cells, a Daly 200A BMS, and a Victron SmartSolar 100/30 doing the charging. The whole lot lives in the back of my Sprinter conversion.

What genuinely surprised me was how different the usable capacity feels compared to the old AGMs. I was getting maybe 60–70Ah reliably out of those 110s before voltage started sagging. Now I'm pulling 200Ah+ without a murmur, and the Victron app just sits there looking smug and green. Ran the van for four days on a cloudy Welsh hillside in February — two 200W panels — and never dropped below 70%.

The one thing I didn't expect was how much time I'd spend tweaking absorption settings. Settled on 14.2V absorption, 13.5V float, 10A tail current on the Victron, and it's been rock solid since. Happy to share the full profile if anyone's running a similar setup.

Anyone else made the jump from AGM to prismatic cells rather than buying a pre-built pack? Curious whether people found the DIY route worth the extra headache, or if something like a Fogstar Drift pre-built would've saved the faff.

Great write-up @WattAMess25! Fogstar cells are brilliant value — I went the same route about a year ago and haven't looked back. One thing I'd add that made a massive difference for me was spending proper time on the cell compression setup. Even a bit of swelling can throw your capacity readings off over time if the cells aren't held snugly together. Did you go with a wooden enclosure or aluminium angle for your build? Also worth keeping an eye on your cell-level voltages during the first few charge cycles — you might find one cell drifts slightly and needs a manual top-balance before your BMS settles into a proper rhythm. Sounds like you've done the hard work though, that AGM/lithium hybrid nightmare is all too familiar! 😄

Really useful thread this — I've been sitting on a similar decision for a while now.

@WattAMess25 what did you use for your BMS in the end? That's the bit I keep going round in circles on. I've got a van conversion with a Victron SmartShunt already in place, and I want whatever BMS I choose to play nicely with the Victron ecosystem rather than fight it.

Also curious — did you build your pack in series, parallel, or series-parallel? I'm looking at 280Ah cells myself but can't decide whether to go 4S for 12V or push to 24V given I'm also using it as an emergency backup at home.

The BMS errors on that secondhand lithium sound familiar. Had something similar on a cheap unit — turned out to be a duff cell dragging the whole pack down.

Really glad this thread came up — I've been down a similar rabbit hole myself. @WattAMess25 one thing I'd add for anyone else reading: don't underestimate the importance of a decent BMS configuration once you've built your bank. I had my cells balanced and wired up nicely but was still getting odd behaviour until I sat down and properly set the charge/discharge cutoff parameters to match my actual usage patterns. Made a massive difference to cycle consistency. @VanKev if you're still on the fence, the Fogstar route does seem to be the sweet spot for cost vs quality at the moment — just make sure you're buying matched cells and doing a proper top-balance before first use. Takes a bit of patience but saves headaches later.

Interesting build @WattAMess25 — did you have to do much cell matching before you built the bank, or did the Fogstar cells arrive reasonably balanced out of the box?

Also curious what BMS you ended up going with. I'm on a boat and the damp environment has killed two cheaper units on me already. Currently eyeing up the Victron Smart BMS but the price jump is significant compared to the JK units everyone seems to recommend.

One thing I'm wrestling with is whether 280Ah is actually enough for liveaboard use without shore power, or whether I'd be better starting with a larger bank from the off rather than expanding later. Did you size yours with room to grow?

Been lurking on this thread for a bit — really useful stuff.

Quick question for @WattAMess25: did you have any issues with your BMS sizing relative to the 280Ah bank? I'm trying to work out whether to go 100A or 150A continuous for a garden office setup (probably 2-3kW loads at peak).

Also wondering whether you went with a Victron SmartShunt for monitoring, or something else? I've seen a few builds where people regret skimping on the monitoring side and then can't figure out why their SOC readings are all over the place.

Trying to plan this properly rather than cobbling something together and spending the next 18 months troubleshooting like you did — no offence meant! 😄