Upgraded to a 200Ah lithium battery in my van — was it worth it?

After two seasons running a 110Ah AGM in my Sprinter, I finally bit the bullet last month and swapped it out for a 200Ah LiFePO4 from Fogstar. Total cost came to around £380 for the battery itself, plus a few hours of my time rewiring and swapping out the old VSR for a Victron Orion-Tr Smart DC-DC charger (another £110 or so). Not a cheap afternoon, but I'd been fed up with the AGM only delivering usable power down to about 50%, so effectively 55Ah of real-world capacity.

The difference has been pretty dramatic, honestly. I've got a 12V compressor fridge drawing around 3-4A average, a couple of USB sockets, and I occasionally run a small inverter for a laptop. With the old AGM I was nervous about back-to-back cloudy days even with my 175W roof panel. Now I'm sitting at 80-90% most mornings after overnight use and the Victron app is showing me exactly what's going on, which I love.

One thing I wasn't expecting — the Orion-Tr has made a massive difference to charging from the alternator on driving days. Previously the VSR was pretty lazy about topping things up. Now even a 90-minute motorway run gets me back to near full.

Has anyone else made a similar switch and noticed anything I should watch out for longer term? Particularly curious whether others have had any BMS issues in cold weather — we're planning a Scottish trip in January.

@CoastalBoater short answer — yes, absolutely worth it 😄

The usable capacity jump is mental when you think about it. Your old 110Ah AGM was realistically giving you maybe 50-55Ah before you started stressing the chemistry. The Fogstar 200Ah? You're looking at 160-180Ah actual usable. That's not double, that's like triple real-world capacity.

I run Fogstar cells in my garden office setup and they've been rock solid. Build quality is genuinely decent for the price point.

One thing to watch — make sure your charger/alternator setup is properly configured for lithium charge profiles. AGM and LiFePO4 have different absorption voltages and you don't want to be undercharging it for years without realising. Worth double-checking your B2B charger settings if you're charging off the alternator. Victron SmartShunt is also a cracking addition if you want proper state-of-charge monitoring.

@CoastalBoater I made almost the identical swap two years ago in my tiny house on wheels — 110Ah AGM to a 200Ah Fogstar Drift — and the moment that really sold it for me wasn't the extra capacity at all.

It was a cold February on a Welsh hillside, watching my Victron BMV-712 hold steady at 98% after a grey, overcast day. The AGM would've been sulking at 60% and complaining about it all night through a dying inverter.

The weight difference also genuinely surprised me. Shifting that old AGM out was a two-person job. The LiFePO4 I carried in myself.

One thing worth mentioning — make sure your alternator charging setup is sorted before you rely on it heavily. I got caught out initially because my B2B charger wasn't rated properly for the lithium charge profile.

Great write-up @CoastalBoater! One thing worth mentioning that nobody's touched on yet — keep an eye on your alternator charging setup. Lithium's low internal resistance means it'll happily pull massive current when depleted, and older Sprinter alternators can struggle with that sustained load. A DC-DC charger (B2B) is genuinely worth adding if you haven't already — Victron's 30A unit is popular but Sterling and Renogy both do decent budget alternatives.

Also worth double-checking your solar controller is lithium-compatible and you've updated the charge profile settings. Easy thing to overlook mid-install excitement! 😄

Running a similar Fogstar setup in my own van for 18 months now and it's been rock solid. The flat discharge curve alone transformed how I use my equipment — no more dim lights warning me I've pushed the battery too hard.

Really useful thread this. @WillowGazer raises a good point about the alternator — worth adding that fitting a proper DC-DC charger (B2B) between your alternator and the lithium is the sensible way to handle this. The LiFePO4 will happily accept charge as fast as you can throw it at it, and without a B2B limiting the current, you're potentially running your alternator hard for sustained periods, especially on shorter drives.

@CoastalBoater did you factor that into your install cost, or were you already running one from the AGM setup? Some folks assume the existing wiring setup carries straight over and get caught out.

The Renogy and Victron 30A units are popular choices and won't break the bank. Makes the whole system work properly together rather than just bolting the new battery in and hoping for the best.

Great thread! @CoastalBoater, one thing I'd add from my own experience swapping out AGMs on the boat — don't overlook your battery monitor. AGMs and LiFePO4 have completely different state-of-charge curves, so your old voltage-based readings will be wildly inaccurate with lithium. A proper coulomb-counting monitor like a Victron BMV makes a massive difference in actually knowing what's going on with your battery. Also worth double-checking your charger profiles — many older leisure chargers don't have a dedicated lithium setting, and repeatedly hitting an AGM absorption voltage on a LiFePO4 isn't ideal long-term, even if the BMS protects you. Small things, but they help you get the full benefit of that upgrade. Sounds like you're already seeing the real-world gains though — that usable capacity difference really does change how you use your van! 🚐

Good shout on the alternator concern @WillowGazer and @MistyMaker — that's already covered so I won't rehash it.

What I'd add, coming from a narrowboat background rather than a van, is state of charge monitoring. With AGM you could roughly gauge health by voltage. LiFePO4's flat discharge curve means voltage tells you almost nothing useful across most of the range — you genuinely need a proper coulomb-counting shunt like a Victron BMV-712 or similar.

Without one you'll think you've got plenty left and then hit the BMS cutoff unexpectedly. Done it myself on the hut setup during a cold spell.

Also worth checking your charger profile if you haven't already — a lot of stock Sprinter converters and mains chargers will still be set to AGM curves. Won't damage the cells immediately but you'll get poor capacity utilisation long-term.

Great write-up @CoastalBoater! One thing nobody's mentioned yet — check your battery monitor if you're still running the one calibrated for your AGM. The charge/discharge curves on LiFePO4 are completely different, so your state-of-charge readings will be wildly inaccurate unless you recalibrate or swap to a monitor that supports lithium profiles. A Victron BMV or similar is worth every penny for actually knowing what's left in the bank. Found this out the hard way on my own van build — thought I had 40% remaining and was nearly flat!