Anyone else using their motorhome battery bank as home emergency backup?

After three power cuts last winter — longest was 11 hours, cheers National Grid — I got fed up and started plugging the house into the motorhome when it's parked on the drive. Running a 200Ah Fogstar lithium bank with a Victron MultiPlus 12/3000, and honestly it handles the essentials without breaking a sweat. Fridge, a couple of lights, phone charging, the gas boiler's control board. That's about it, but that's all we actually need.

The setup works, but it feels bodged. I'm running a proper 16A hookup cable between the van and the house consumer unit via an interlock — nothing illegal, I've had an electrician friend look it over — but I know I'm asking the battery to do two jobs now. Regular motorhome trips mean I can't just leave it permanently wired in.

Has anyone built something a bit more deliberate for this dual-purpose use? Wondering whether a second dedicated battery bank in the garage makes more sense, or whether others just accept the "van on the drive = backup power" compromise and manage the logistics around it. Also curious what capacity people reckon you actually need for a typical UK winter power cut of, say, 12–16 hours.

Ella1994 | 47 posts

@ExmoorCamper great shout, we do exactly this! One thing worth mentioning that I don't think's been covered — get yourself a proper transfer switch or at minimum make absolutely sure you're disconnected from the grid before backfeeding through your consumer unit. Sounds obvious but it's genuinely dangerous for linesmen working on the fault if you haven't isolated properly.

We use a simple interlocked changeover switch (about £35 from Amazon) wired in by our sparky, keeps everything above board. Also worth noting the Fogstar cells handle the occasional deep cycle fine but try not to make a habit of draining below 20% if you want decent longevity out of them. How are you connecting to the house — extension lead into a socket, or something more permanent?

VoltChloe | 203 posts

Worth flagging — if you're on a standard tariff, running your motorhome/boat battery bank as home backup sits in a grey area with your DNO (Distribution Network Operator). Not illegal, but worth checking whether your installer needs to notify them if you're doing anything beyond a simple extension lead setup.

I do something similar on the narrowboat when it's moored at home — Victron Multiplus makes the transition seamless. The bit most people overlook is cable sizing between the vehicle and house consumer unit. A lot of folk grab a long extension lead that's totally underrated for the loads they're actually pulling, especially if a fridge compressor kicks in at the same time as something else.

What gauge are you running for the connection, @ExmoorCamper?