Fitting a 200Ah lithium under the bed in a Fiat Ducato — clearance issues and BMS wiring questions

Finally pulled the trigger on a 200Ah LiFePO4 (the Fogstar Drift, since everyone here seems to rate them) and I'm now lying on the floor of my L3H2 Ducato wondering how on earth I'm going to make this fit. The space under the fixed bed is about 280mm floor to slat, and the battery itself is 240mm tall — so in theory there's enough room, but by the time I account for the cable connections on top I'm already tight. Has anyone shimmed the bed frame up slightly, or is that just asking for trouble structurally?

The other thing I'm not sure about is the BMS wiring. I've got a Victron SmartShunt and a 30A DC-DC charger (Renogy, nothing fancy) going in alongside it. The Fogstar's built-in BMS handles the protection side, but I want to run a separate fuse as close to the positive terminal as possible — currently thinking a 300A ANL inline fuse on a short 70mm² run to the busbar. Does that sizing sound right, or am I over-speccing the fuse relative to the DC-DC charger's actual draw?

Happy to share photos of the install once it's done — the Ducato seems to be the van everyone's working with lately so hopefully it'll be useful for someone.

Good shout on the Fogstar Drift, @Chris1984 — solid choice. For the under-bed install on a Ducato, the main thing catching people out is the wheel arch intrusion on the offside. Measure twice before you commit to a position because there's often less flat floor than it looks.

For BMS wiring, keep your positive and negative runs as short and equal in length as possible, and make sure you're fusing close to the battery terminals — within 300mm ideally. The Drift's built-in BMS is fairly capable but I'd still run an external low-voltage cutoff to protect it during storage.

What's your current cable routing plan for getting the feeds up to your consumer unit? That often determines where the battery ends up sitting more than the physical clearance does. Happy to help once you've got measurements.

@Chris1984 — worth checking whether your bed platform has a removable panel on the side rather than only accessing from the top. Mine in a similar Ducato layout had one hiding behind a bit of trim that gave me just enough room to angle the battery in without dismantling everything.

On the BMS wiring — are you planning to connect the BMS alarm output to anything, or just leaving it floating? I've been going back and forth on whether to wire mine into a Victron BMS 12/200 or just rely on the Fogstar's internal BMS and keep it simple. Would genuinely help to know what route others have gone down before I commit to drilling more holes than necessary.

What's your charging setup — solar only or are you also running a B2B from the alternator?

Don't forget the Ducato floor has a lovely habit of flexing just enough to make your perfectly measured battery fit like a drunk uncle trying to squeeze into last year's Christmas jumper.

@Chris1984 one thing nobody's mentioned yet — the Fogstar Drift has its BMS comms port on the short end, so plan your cable routing before you slide it into the void. I made the mistake of positioning mine terminals-first against the rear wall and then realised I couldn't get a straight run to the Victron SmartShunt without a nasty bend radius on the cable.

Also worth measuring the lip on your bed frame rather than just the open floor space — there's often a 20–30mm overhang that Fiat don't mention anywhere useful. The Drift's 218mm height caught me out on that exact point.

Strap it down properly too; those cells absolutely do not want to be sliding around on cornering. Two ratchet straps through the floor tie-down slots sorted mine nicely.

@Chris1984 good shout on the Fogstar Drift, solid bit of kit. One thing worth thinking about with the under-bed install — make sure you're leaving adequate ventilation around the battery even though LiFePO4 is far safer than AGM. More practically, run your positive cable with an ANL fuse as close to the battery terminal as physically possible, ideally within 300mm. A lot of people route the cable all the way to their fuse box before protecting it, which defeats the purpose entirely if you've got a fault partway along. Also worth considering a small wooden cradle to keep the battery from shifting on those lovely French autoroute surfaces — the Ducato chassis transmits road vibration surprisingly well under there.