Finally wired up a 200Ah LiFePO4 in the Transit – a few lessons learned the hard way

Been meaning to post this for a while. Spent most of last weekend fitting a 200Ah LiFePO4 battery (Fogstar Drift, for anyone wondering) under the bed in our 2018 Transit LWB. Replaced the old 110Ah AGM which was genuinely on its last legs – barely holding 80Ah by the end. The difference in usable capacity is night and day, obviously, but the install itself threw up a few surprises I wasn't expecting.

Biggest headache was the BMS communication with my existing Victron SmartShunt. The shunt kept reading the battery as fuller than it actually was for the first few cycles – took about three full charge/discharge cycles before the SOC percentage started behaving itself. Also had to re-crimp one of my 70mm² cable runs because I'd used the wrong ferrules first time round and got a tiny bit of voltage drop under load. Nothing dangerous, just annoying.

Currently running 400W of solar on the roof (two 200W panels in series into a Victron 100/30 MPPT) and a 30A DC-DC charger off the alternator. On a decent sunny day in Wales last week I was pulling 18-22A pretty consistently through the afternoon, which felt pretty decent for March. Managed three nights without shore power running the diesel heater, a 60W fridge, and lights without dropping below about 40% SOC.

Has anyone else found the Fogstar Drift takes a while to "bed in" with a SmartShunt, or is that just a general LiFePO4 quirk? Also curious whether anyone's bothered adding a battery monitor display separate from the Victron app – wondering if it's worth the extra dash clutter.

@MickDavies interesting you went with the Fogstar Drift — I've been eyeing that one up for my Transit conversion. Did you have any issues with the BMS tripping during high-draw moments, like running a kettle or hair dryer?

Also curious what you used for your DC-DC charger? I'm currently trying to decide between the Victron Orion-Tr Smart and a cheaper Renogy alternative. The price difference is pretty steep but I've heard the Victron handles alternator load much better on modern Transits with their smart alternators.

What gauge cable did you run from the starter battery location? I've been going back and forth on whether 16mm² is sufficient or whether to bump up to 25mm².

@MickDavies good shout on the Fogstar Drift — solid bit of kit for the money. One thing I'd flag from my own experience: if you're planning to charge from the alternator, make sure your B2B charger is properly rated. I underspecced mine initially and it struggled badly once I started pulling current for EV pre-conditioning when parked up.

Also worth double-checking your cable run lengths and factoring in voltage drop properly — LiFePO4 will absolutely let you pull more current than AGM ever did, and undersized cables get warm fast.

What Victron kit did you end up going with, or are you running a different MPPT setup? Curious whether you've integrated any monitoring — the Victron Cerbo GX is overkill for some but genuinely useful if you're doing serious loads.

Great write-up @MickDavies, looking forward to reading the full lessons learned! One thing I'd add that caught me out on my own LiFePO4 install — make sure your alternator charging setup has a proper DC-DC charger (B2B) in the circuit rather than just a split charge relay. LiFePO4 will happily drag your alternator into thermal shutdown trying to fill itself at full current. A decent Sterling or Victron B2B will regulate that nicely. Also worth double-checking your fusing is sized correctly close to the battery terminals — LiFePO4 can deliver enormous fault currents compared to AGM. Sounds like you've gone with a quality battery there, the Drift gets decent reviews for the price point.

Great thread @MickDavies, keen to hear the full write-up! One thing worth mentioning that I don't see flagged yet — when you swapped from AGM to LiFePO4, did you update your battery type setting on the B2B charger (if you're running one from the alternator)? Easy to overlook and it can cause all sorts of odd charging behaviour. Also worth double-checking your low voltage disconnect threshold if you've got one set — AGM cutoffs are way too conservative for LiFePO4 and you'll be leaving usable capacity on the table. The Fogstar Drift is a cracking choice for Transit builds by the way, great value per Ah compared to some of the better-known brands. How are you finding the physical fit under the bed — any clearance issues with the BMS terminals?

@MickDavies good stuff. One thing nobody's mentioned yet — cable sizing. Swapping from AGM to LiFePO4 means your BMS can deliver current fast when it wants to. If your existing cabling was sized for a lazy old AGM, you might find yourself with warm wires or a nuisance trip under load.

Learned that the painful way in my cabin setup before I sorted the van. Undersized tails between the battery and busbar got properly toasty running the compressor fridge.

Also worth checking your DC-DC charger if you're charging off the alternator — Victron Orion-Tr Smart is the go-to for good reason. Transit alternators don't love being hammered by a LiFePO4 demanding full current.

Fogstar Drift is cracking value though. Running mine nearly 18 months, zero drama.

@Curly38 makes a fair point on cable sizing, but the one that bit me hardest during my own Transit build was state of charge display accuracy.

Spent three days convinced my Fogstar was performing poorly — turned out my old voltage-based gauge was reading the flat LiFePO4 discharge curve completely wrong. Showed 60% when it was genuinely at 15%.

Binned the voltage gauge, fitted a Victron BMV-712, and suddenly the whole picture made sense. Proper coulomb counting is non-negotiable with lithium; you're essentially flying blind without it.

Also worth noting — if you're running any mains inverter off that 200Ah, double-check your BMS continuous discharge rating against your inverter's peak draw. The Fogstar Drift handles it well, but complacency there can trigger some very confusing shutdowns at inconvenient moments.

@TorJake curious what SOC issue caught you out — I'm guessing a voltage-based display reading confidently at "80%" while the BMS was quietly throttling discharge?

Worth adding for @MickDavies — your B2B charger (if you're running one off the alternator) needs checking too. A lot of the older Sterling and Victron Orion units have LiFePO4 profiles but the absorption voltage ceiling varies. Get that wrong and you're either undercharging chronically or hammering the top of the cells on long motorway runs.

Learned this the hard way running EV charging experiments off a similar setup — the charging profile matters far more with LiFePO4 than it ever did with AGM.