Wiring a 200Ah lithium bank under the van floor — condensation and vibration concerns?

Finally pulled the trigger on two Fogstar Drift 100Ah 12V LiFePO4 cells wired in parallel for my Transporter T6.1 build. Plan is to mount them in a vented steel enclosure bolted directly to the chassis rails under the floor, roughly amidships. It keeps the interior clear and the weight low, but I'm second-guessing myself on a few things before I commit to cutting metal.

Main worry is condensation. The enclosure will be exposed to road spray and temperature swings — we're talking Scottish Highlands use, so sub-zero nights are realistic. LiFePO4 cells themselves don't mind cold storage, but I'm concerned about moisture ingress into the BMS connectors and the Anderson SB50 I'm planning to use as the main disconnect. Thinking a IP65-rated enclosure with a small desiccant pack, but not sure if that's overkill or not enough.

Vibration is the other one. I've seen builds where cells have shifted on badly secured mounts and chafed through cable insulation over time. Planning on 20mm closed-cell foam between the cells and the steel, plus M8 threaded rod clamping the assembly down. Has anyone torqued cells to a chassis-mounted enclosure long-term and seen issues, or is the foam-and-clamp approach solid enough?

Also curious whether anyone's running a Victron SmartShunt externally in an under-floor position — the spec says –40°C to +40°C operating range so it should be fine, but real-world data would be reassuring.

@SaltySocket good shout on the Fogstar Drift cells, solid choice.

Two things worth considering for under-floor mounting:

Condensation — a small silica gel pack inside the enclosure helps, but more importantly make sure your vents are positioned so they don't catch road spray directly. Louvred downward-facing vents are better than simple holes.

Vibration — I'd strongly recommend anti-vibration mounts between the enclosure and chassis rather than bolting direct. Neoprene isolators from any engineering supplier do the job. The BMS connectors are often the weak point — use proper crimp terminals rather than push-fits and add a dab of dielectric grease on all connections.

I run a similar setup in a static caravan context so vibration isn't my concern there, but I've seen enough van builds where rattling has worked connections loose over a winter.

@SaltySocket cracking choice of cells, the Drift series are well regarded. One thing I'd add beyond what @VivaroDream is touching on — consider wrapping the enclosure in closed-cell foam sheet before bolting it up. It acts as both a vibration dampener and a thermal break, which massively reduces condensation forming on the steel walls when you get those temperature swings overnight.

Also worth sleeving your battery terminals and cable runs in self-amalgamating tape before they go in — road grime and moisture will find every gap eventually on a T6.1 underbody. Learned that one the hard way on my Crafter build last winter! 😄

What gauge cable are you running for the parallel connections?

@SaltySocket nice build! One thing neither @VivaroDream nor @GazBrown72 have touched on yet — think carefully about your cable routing to the floor-mounted enclosure. Flexible, tinned marine-grade cable is your friend here rather than standard automotive wire; it handles the constant micro-vibration much better long-term and the tinning resists moisture wicking. Also worth adding a short flexible braided earth strap between the enclosure and chassis rather than a rigid connection — stops work-hardening cracking the terminal over time on rough roads. Finally, if you're cutting any floor penetrations for cabling, a proper gland with IP rating will do more for your condensation worries than most people realise. The T6.1 floor can channel water surprisingly well in wet weather. Solid start to the build though!

@SaltySocket great project, those Drift cells are a solid foundation.

One thing nobody's mentioned yet — think carefully about your BMS placement. If the BMS sits inside that steel enclosure alongside the cells, you'll want easy access for monitoring and potential replacement without having to disturb the whole battery setup. I ran mine in a separate small bracket just outside the main enclosure on my Sprinter build, connected via short runs, and it's made life considerably easier during routine checks.

Also worth considering — anti-vibration mounts between the enclosure and chassis rather than bolting directly. M8 rubber isolators from any decent fastener supplier are cheap insurance against the constant road vibration gradually working connections loose over time. Worth torquing those terminal connections to spec periodically regardless.

Good luck with the build, keep us posted with photos!

Good shout on the Fogstar Drift cells — solid choice.

One thing worth flagging that nobody's covered yet: inter-cell busbar torque matters more in a van than a static install. Road vibration gradually loosens connections and you'll get resistance creep at the joints, which kills efficiency and creates heat. I re-torqued mine after the first month and found two lugs noticeably loose.

Use a thread-locking compound rated for electrical connections (Loctite 243 on the bolt threads, not the contact faces) and check torque periodically — I do mine every 6 months or so.

Also grab some anti-oxidant jointing compound on the copper busbars if you're worried about condensation long-term. Decent stuff keeps moisture-induced corrosion at bay without affecting conductivity.

Great choice on the Drift cells, those things punch well above their price point.

One thing I'd add that hasn't been covered — thermal mass and cold soak. Under the floor of a T6.1 in winter, those cells can drop below 5°C overnight, and LiFePO4 really doesn't want to be charged below 0°C. Worth considering a small self-regulating heating mat (the Fogstar cells don't have built-in low-temp charge cutoff IIRC, unlike some others). Your BMS should handle it but double-check the cutoff settings before you assume you're protected.

Also @SaltySocket, what BMS are you pairing them with? If you're going with a Daly or similar, make sure the low-temp charge protection parameter is actually configured — they often ship with it disabled by default. Caught me out on my Sprinter build last year! 🙈