Got caught out by a 3-day grid outage last winter — here's what I learned about backup EV charging

Had three days without grid power back in January during that cold snap that hit the Midlands hard. I've got a 10kWh Fogstar Drift LiFePO4 bank paired with a 3kW Victron Multiplus-II and about 2.4kW of panels on the roof. Normally more than enough for the house. What I hadn't properly planned for was the EV sitting on the drive needing juice — a 2022 Nissan Leaf that the wife uses for work runs on a 7kW home charger obviously throttled back to whatever the Victron could manage via AC coupling.

The Multiplus handled it reasonably well in the end, but I had to manually drop the charge rate right down to 6A using the EVSE settings just to keep the system from collapsing overnight when solar input dropped to near zero. Battery was sitting at around 40% SoC by morning on day two, which made me properly nervous. The Leaf's onboard charger doesn't play nicely with fluctuating voltage either — kept throwing a fault and dropping the session.

What I've been thinking about since is whether a dedicated DC-coupled EV charging solution would've handled this better, or whether the answer is just more battery capacity. I've seen some chat about using a second smaller Victron MPPT to feed a CHAdeMO adapter directly but I can't find anyone who's actually done this with a Leaf in an off-grid scenario in the UK specifically.

Has anyone here actually stress-tested their backup setup with simultaneous EV charging demands, particularly over multiple days? What's your minimum viable battery bank size if the EV is non-negotiable?

@RetiredSquaddie three days is no joke in January, especially in the Midlands — that cold snap was brutal.

The EV charging piece is what catches most people out. Even on "slow" Mode 3 charging, a Type 2 cable at minimum 6A is still pulling 1.4kW continuously, which will absolutely hammer a 10kWh bank overnight.

What I've done for the garden office setup is configure a dedicated Victron DVCC limit so the Multiplus-II won't export more than 500W to the "EV circuit" when grid is absent. Keeps the lights and heating prioritised.

For the motorhome I've wired a simple 13A commando socket fed via a relay that only closes above 80% SoC — crude but effective.

Worth looking at the Victron ESS assistant settings specifically — there's a Grid lost action that most people leave at default but really shouldn't.

Really interesting thread @RetiredSquaddie — the EV charging question is one I've been wrestling with myself.

One thing worth considering is whether your Multiplus-II could handle a trickle charge scenario. If your EV supports it, dropping to 6A on a Type 2 lead works out at roughly 1.4kW — well within your inverter's capacity, though obviously it'll hammer your battery bank over any meaningful period.

The maths get uncomfortable fast in winter when your solar yield is already poor. I'd be prioritising knowing exactly what your vehicle's minimum charge rate is before assuming trickle charging is even viable — some cars won't negotiate below 10A.

Personally I've started keeping a rough "EV emergency protocol" written down — what journeys are essential, nearest rapid charger that's likely to have power (petrol station forecourts often do), and at what battery percentage I'd actually bother attempting a charge at home.