Can you charge an EV from a static caravan battery bank without killing it?

Been mulling this over for a while. I've got a 24V LiFePO4 bank (4x Fogstar Drift 200Ah cells) in my static, currently used for general loads and topped up via a 600W array. Works a treat for day-to-day stuff, but I'm wondering about occasionally tapping it to top up my EV when I'm on site rather than running a long mains extension from the park hookup.

Not talking a full charge — more like a 10–20% top-up on a small EV (Nissan Leaf, 40kWh pack). Even that's a big ask though. Rough maths says 10% of 40kWh is 4kWh, which is most of what my battery bank holds at usable depth of discharge. Worried about high sustained discharge rates wrecking the cells or the Victron MultiPlus I'd need to invert through.

Has anyone actually done this, or is it one of those ideas that sounds plausible but destroys kit in practice? Particularly curious whether the C-rate on Fogstar Drift cells can handle it, and whether a MultiPlus 24/3000 would be the right inverter/charger to look at.

SolarOwen | 847 posts

@TelHall Short answer: technically yes, but your bottleneck is going to be charge rate rather than any harm to the cells. LiFePO4 handles high discharge beautifully, so no drama there.

The real question is what EV you're talking about and whether you're using a standard 3-pin lead. A typical Mode 2 cable draws around 10A, so roughly 2.3kW — your 24V bank at that discharge rate is actually quite manageable for a reasonable session.

What you will find is recovery time. Your 600W array isn't going to refill that bank quickly after a decent charging session, so you're essentially running a deficit unless you've got good solar days ahead.

Worth looking into a Victron SmartShunt if you haven't already — knowing your actual state of charge before you plug in makes the whole thing much less of a gamble.

@TelHall mate your Fogstar bank would laugh at general loads then absolutely weep when an EV rocks up demanding 7kW — that's like asking a narrowboat battery to tow a cruise ship 🚢

Your 4×200Ah at 24V gives you roughly 19.2kWh usable (being generous), whereas even a "top up" EV charge eats several kWh before it even says thank you.

The C-rate is your real killer — check what continuous discharge current those Drift cells will actually sustain vs what your charger demands.

Honestly, solar input vs EV output maths just doesn't work unless you're talking overnight slow-trickle via something like a Victron Multiplus with serious rate-limiting. Done similar sums on my static setup and quietly put the idea back in the drawer. 🗄️

@TelHall this is something I've been genuinely curious about for my own setup too! On the boat I run a similar-ish bank and the maths on EV charging always makes my head spin a bit.

Quick question though — what inverter are you running between the bank and any potential EV charger? Because even if the cells themselves can technically handle the discharge rate, most affordable inverters will throw the towel in well before you get anywhere near usable EV charging speeds.

Also worth thinking about state of charge recovery — your 600W array after a big EV dump could take days to claw back. Have you considered a grid-tied top-up arrangement alongside the solar, or is this fully off-grid?

I'd love to know if anyone's actually done this with a Victron Multiplus setup in practice rather than just theoretically.

OllieRoss74 | 312 posts

@TelHall I ran a similar thought experiment when I was speccing out my shepherd's hut setup. The maths is the real villain here — your 800Ah at 24V gives you roughly 19kWh usable (at 80% DoD). A modest 7kW home charger would drain that in under three hours, and you'd be sat waiting days for your 600W array to claw it back.

What actually works is the "overnight trickle" approach — use a small EVSE capped right down to 6A via a Victron MultiPlus, top the car up slowly rather than treating your bank like a rapid charger. You're never going to drive to Edinburgh, but keeping commuter miles topped up? Genuinely doable.

The battery won't die — LiFePO4 handles the discharge cycles fine — but your solar harvest becomes the bottleneck, not the chemistry.