Sizing a leisure battery bank for EV top-up on a week-long wild camp — where's the sweet spot?

Planning a week off-grid in the van later this summer and want to experiment with using the leisure bank to do small opportunity top-ups on my Nissan Leaf (24 kWh, older gen). Not trying to fully charge it — just add 5–10 miles range each morning to extend my radius for day walks.

Currently running 2× 200Ah Fogstar Drift LiFePO4 in the van (400Ah, 12V), fed by 400W of roof solar and a Victron SmartSolar 100/30. On a decent July day in Suffolk I'm typically seeing 150–180Wh recovered per 100W panel, so roughly 600–720Wh usable from solar alone. The Leaf's onboard charger pulls around 3.3 kW via a Type 1 inlet, which obviously wants 240V AC — so I'd be inverting via a Victron MultiPlus 12/3000. Rough maths says even a 20-minute charge session would pull around 1.1 kWh from the bank, which is a meaningful chunk of 400Ah at 12V (4.8 kWh usable at 80% DoD).

Has anyone actually done this in practice — van-to-EV trickle charging off a leisure bank without wrecking your SOC for the evening? Wondering whether the sensible floor is "only charge the Leaf if bank is above 80% SOC by 10am" or whether people use a more sophisticated trigger. Also curious if a second 200Ah Fogstar is genuinely worth the boot space versus just accepting shorter EV excursions.

Ollie1991 | 847 posts

@SuffolkExplorer interesting experiment! Worth being realistic though — a 24kWh Leaf versus a practical leisure bank is a tough ask. Even a beefy 400Ah LiFePO4 at 48V only gives you roughly 19kWh total, and you'd never want to pull it below 20% SOC, so realistically 15kWh usable — and that's before your van's own consumption is eating into it daily.

The sweet spot I'd suggest is sizing for meaningful range anxiety relief rather than proper charging — maybe 10-15 miles worth per top-up. Factor in your solar harvest too; a decent 600W roof array in July can genuinely recover things overnight.

What's your current bank setup and roof space looking like? That'll massively change the calculation before anyone starts throwing numbers around.

DodgyCaptain | 203 posts

@SuffolkExplorer curious about this from a narrowboat angle — we face similar "opportunity charging" decisions with engine alternators. One thing worth thinking about: what inverter are you planning to push the charge through? The Leaf's onboard charger will likely draw 3.3kW minimum, so you need an inverter that can sustain that continuously without throttling back due to heat or voltage sag. What's your current inverter spec?

Also, are you accounting for the conversion losses? Battery → inverter → AC → Leaf onboard charger → Leaf battery. You're realistically looking at 80–85% round-trip efficiency at best, so whatever you think you're putting in, budget for losing 15-20% along the way.

What does your solar top-up look like during the week? That changes the bank sizing calculation significantly.

Done a bit of EV-from-van dabbling myself so here's the reality check:

Even a chunky 400Ah 24V LiFePO4 bank (Fogstar cells work well) gives you roughly ~9.6kWh usable — that's barely 40% of your Leaf's pack in ideal conditions, and you're losing another 10-15% to inverter inefficiencies.

Key snag is inverter surge — a Type 2 EVSE pulling 3.6kW minimum will hammer your system hard. You'd need a decent 5kW pure sine inverter minimum (Victron Multiplus territory).

Realistic expectation for a week's camp:

• Top up maybe 20-30 miles range total across the week
• Pair with a 500W+ solar array to replenish during the day
• Treat it as range anxiety buffer, not actual charging strategy

Worth it as an experiment? Yeah probably. Worth sizing your bank around it? Honestly no — tail wagging the dog territory.

WezFrost | 312 posts

@GeoffRobinson covered the numbers well so I'll skip repeating that. One thing nobody's mentioned — your inverter matters massively here. Leaf's onboard charger will want a clean sine wave and decent surge capacity. Loads of folk slap a cheap modified sine inverter in and wonder why things go weird.

Also worth checking what the Leaf actually draws at minimum charge rate. On the older 24kWh gen it's not massively flexible — you can't always throttle it right down like some newer EVs.

From my boat setup (280Ah LiFePO4, Victron MultiPlus) I've done small EV top-ups and the Victron handles it cleanly but it's still a noticeable hit on the bank. Factor in your solar recovery time realistically, not optimistically — week-long wild camps rarely give you textbook harvest days.

@GeoffRobinson makes the good points on capacity, but worth flagging the inverter side too — a Leaf's onboard charger wants a clean, stable 230V sine wave and will throw a wobbly with anything marginal.

Been there with emergency backup testing; even brief voltage sags under load can trigger the EVSE to fault out. A proper pure sine inverter (Victron Multiplus territory) is non-negotiable really.

Also consider your charging rate ceiling — the Leaf's OBC is 3.3kW on older 24kWh models, so you're pulling that continuously. Match your inverter and your battery C-rate accordingly, or you'll cook either the bank or your week away.

Small top-ups are totally doable but the kit needs to be right-sized from the start.

Good shout from @LDVSolar on the inverter — I'd add that on my own van setup I ran a Victron Multiplus 12/3000 and even that occasionally threw a wobbly with certain EVSE handshake timing. Worth checking your inverter's pure sine output is genuinely clean under load, not just rated for it.

The other thing I'd flag specifically for the Leaf 24 is that charging below ~20% SOC on an older pack hammers the cells harder, so if you're only doing small top-ups anyway, target keeping it between 40–80%. That changes your actual required kWh per session meaningfully and might let you get away with a smaller bank than you'd initially calculate.

Week-long wild camp though — I'd still not go below 200Ah at 48V if solar input is modest.

DriftGal | 847 posts

Something nobody's quite nailed yet: the Leaf's onboard charger will negotiate a charge rate with the EVSE, and a cheap inverter-charger combo may not handshake cleanly with it. I learned this the painful way when my tiny house build was still running an unbranded 2kW inverter — the Leaf simply refused to begin charging at all.

Worth specifying a proper Type 2-compatible EVSE (even a portable one like an Ohme or Hypervolt Go) between your inverter output and the car. That handshake matters enormously on older Leafs particularly.

Dizzy83 | 1,204 posts

Picking up on what @DriftGal's hinting at — worth knowing the older 24kWh Leaf's onboard charger draws around 3.3kW continuously once it's negotiating full rate. Over a typical wild camp scenario you're realistically looking at short evening sessions rather than meaningful range gains. My suggestion: don't think in terms of "charging the Leaf" at all — think about replacing 3–5 miles of buffer capacity each day. That reframes your battery bank sizing completely and makes the maths far less daunting. A 400Ah 12V bank with decent solar replenishment can handle that without flogging itself silly.

Good point from @DriftGal on charge rate negotiation — worth adding that the AC coupling losses stack up fast here. You're looking at roughly 85–90% efficiency through a decent inverter, then another 85–92% through the Leaf's onboard charger. Multiply those together and you're losing 20–25% before any electrons hit the traction pack. So if your leisure bank is sized around "I need 5 kWh into the Leaf," you actually need to plan for 6–6.2 kWh drawn from the battery. Factor that into your Fogstar or similar LiFePO4 sizing before committing to a bank capacity.

Really useful thread this. One thing I'm curious about that hasn't been fully addressed — what's the realistic depth of discharge you'd want to stick to on the leisure bank during those top-up sessions?

Like, if I'm running a 400Ah LiFePO4 bank (Fogstar cells in my setup), am I looking at capping each EV session at say 20-25% DoD to leave headroom for the van's own loads overnight? Feels like that constraint might be the actual limiting factor on how much you can realistically push into the Leaf each day, more than the charger negotiation side of things.