Anyone running 200Ah LiFePO4 in a Transit-based van — what BMS are you using?

Finally pulled the trigger on two 100Ah Fogstar Drift batteries wired in parallel for my Transit Custom build. Got them mounted under the bed, all good so far.

Thing is I'm second-guessing my BMS situation. The Drifts have built-in BMS obviously, but I've seen people adding an external one on top — Victron BMS 12/200 or similar. Is that overkill when the cells already have protection built in, or is there a genuine reason to do it?

Running a Victron SmartShunt for monitoring and a 40A DC-DC charger from the alternator. Worried mainly about over-discharge protection if I'm away for a few days with no shore power or solar top-up.

Worth adding the external BMS or just trust the Fogstar units to handle themselves?

@OllieThompson73 the Fogstar Drifts have a built-in BMS already — that's literally the point of buying them over bare cells. You don't add another BMS on top.

What you probably want is a proper battery monitor so you can actually see what's going on — Victron BMV-712 is the go-to, does Bluetooth, works a treat. I've got one on my LiFePO4 setup and it's worth every penny.

If you're running parallel though, make sure your cable lengths from each battery to the busbar are identical — otherwise one battery ends up doing more work than the other and you'll get imbalanced state of charge over time. Classic mistake.

What are you using for charge control? That matters more than your BMS situation right now.

@OllieThompson73 worth knowing that even with the built-in BMS on each Drift, when you parallel two of them you can get imbalances between the packs over time — each BMS is only managing its own battery. I ran a similar setup in my Sprinter for about eight months before I noticed one pack was consistently doing more work than the other.

Might be worth looking at whether your charge sources (alternator, solar, hook-up) are set to the correct LiFePO4 charge profile. A lot of problems people blame on the BMS are actually down to a dodgy Victron MPPT setting or the B2B charger not being configured right. What are you using for alternator charging?

@OllieThompson73 — @VitoProject is right that each Drift handles its own cell protection, but the thing worth adding is that Fogstar actually recommend their batteries are suitable for parallel use precisely because the internal BMS on each unit manages independently. That said, I'd still suggest picking up a decent battery monitor like a Victron BMV-712 if you haven't already — it won't replace the BMS functionality but gives you proper visibility across the whole bank (SOC, current in/out, historical data etc). Really invaluable when you're trying to figure out whether your solar or alternator charging is behaving correctly. What's your charging setup looking like? If you're running a B2B charger off the Transit's alternator, make sure it's properly rated for the combined capacity.