Anyone else running a small lithium bank purely for emergency backup in their van?

Got a 100Ah Fogstar Drift LiFePO4 sat under the passenger seat in the Transit. Not my daily driver — it's more of a cabin-on-wheels for the occasional weekend. Runs a 12V compressor fridge, a few USB points, and some LED strips. Nothing mad.

The thing is, I sized it for worst-case rather than regular use. Paired it with a Victron SmartSolar 100/20 and two 175W panels on the roof. Most of the time it barely touches 50% DoD even after a cloudy weekend.

Wondering if anyone else has gone down this route — deliberately overspecced for reliability rather than squeezing every penny out of efficiency. Did you find it overkill, or does that headroom actually pay off when the weather turns grim for a few days?

XAC_Solar | Posts: 847

@WonkyWelder Similar setup here — had a 100Ah LiFePO4 tucked in a Sprinter for a couple of years doing exactly that role. One thing worth thinking about if it's sitting unused for weeks at a time: store it at around 50% state of charge rather than leaving it topped up. LiFePO4 is pretty forgiving but it'll thank you long-term.

Also worth checking your B2B charger settings if you're topping it up from the alternator — some older charge profiles assume lead-acid and can confuse the BMS. A decent battery monitor like a Victron BMV pays for itself just for the peace of mind when you're trying to work out what's actually left before bed. What are you using to charge it currently?

JohnChapman | Posts: 312

@WonkyWelder Nice setup — the Fogstar Drift is a solid choice for that kind of occasional-use scenario. One thing worth considering with a bank that sits idle between weekends: LiFePO4 is quite happy being stored at a partial state of charge (around 50-60% is ideal), so don't feel obliged to keep it topped up to 100% between trips. That'll actually extend the cell longevity over time.

Also worth checking your B2B or charging source is genuinely compatible with lithium charge profiles — it's a detail that catches people out when they've previously run AGM. What are you using to charge it from the alternator, if anything?

BayJason | Posts: 1,203

One thing I'd flag that nobody's mentioned — LiFePO4 sat idle for months at a time wants to be stored at around 50% SoC, not fully charged. If you're leaving the Transit parked up between weekends with the BMS keeping it topped up via a trickle from the alternator or a solar panel, you could be holding it at 100% for weeks. Fine short-term, but not ideal for long-term cell health.

Also worth checking whether that Fogstar Drift has low-temp charge protection built in. Some of the entry-level cells do, some don't. If you're parking up in winter and a cheap charger kicks in at 2°C, you can cause lithium plating.

Not trying to be alarmist — the Drift is decent kit — just the two things I'd verify given it's an infrequently used setup.

BoxerCamper | Posts: 2,156

Running almost identical on my old Boxer — hence the username, obviously. The "emergency backup that never gets used" is basically the van owner's version of a spare tyre.

One thing worth adding: if yours is sat for months like mine was, a Victron IP65 charger on a timer plug sorted my storage maintenance beautifully. Kicks in once a fortnight, tops it up to 80%, job done.

@BayJason is right about idle LiFePO4 — storage charge matters more than people think. I learned that the hard way after a winter of neglect left my Fogstar in a strop and refusing to wake up gracefully.

Also worth knowing: if the van lives outside in a British winter (so, always), low-temperature cutoff on the BMS could catch you out when you actually need that emergency power. Check your BMS specs.

AGM_Pro | Posts: 847

@BayJason makes a good point about storage — worth flagging that if you've got a Victron BMS or even just a basic battery monitor, setting a low-SOC alert before you park it up for weeks saves a lot of grief.

Quick question for the thread though — is anyone using a trickle charger on these during long storage periods? My narrowboat setup runs a Victron IP22 on a timer but I'm unsure whether that approach translates well to a van sitting on a driveway. Does the Drift have any issues accepting a conventional maintenance charge, or does it need something LiFePO4-specific? I've seen some cheaper chargers allegedly "support" lithium but the charge curves look dubious when you dig into the specs.