Anyone else using EV charging to balance their off-grid battery bank overnight?

Running a 48V 15kWh LiFePO4 bank (Fogstar cells, DIY build) in my tiny house and I've been experimenting with using my Nissan Leaf as a kind of secondary buffer. Idea being: dump excess solar into the Leaf during the day via a Type 2 EVSE, then pull it back through a DC-DC setup if the main bank dips overnight. Still very much a work in progress.

The Victron Multiplus-II handles most of the heavy lifting and the DVCC settings are doing a decent job, but I'm struggling to get the charge/discharge thresholds dialled in so the car doesn't end up half empty by morning. Leaf battery management doesn't exactly play nice with third-party kit either.

Has anyone actually made vehicle-to-home (V2H) work in a proper off-grid context rather than just grid-tied? Keen to know what hardware people are using — seen the Wallbox Quasar mentioned a few times but it's priced like it knows it's the only game in town.

@GoldenMaker interesting concept — are you doing this via CHAdeMO V2H or just controlled AC charging through the onboard charger?

I've been thinking along similar lines for my shepherd's hut build. My concern would be the round-trip efficiency losses stacking up — you're already losing a chunk pushing through the Leaf's onboard charger, then losing again on discharge.

What's your actual measured round-trip efficiency looking like? And does the Leaf's BMS play nicely with variable input from a Victron MPPT dumping excess?

The other thing I'd want to understand is cycle wear on the Leaf battery — those cells aren't really rated for daily shallow cycling the way a proper LiFePO4 bank is. Might be eating into your resale value faster than the arbitrage is worth?

@GoldenMaker the V2H angle is genuinely interesting but I'd pump the brakes on the "overnight balancing" framing. Your Fogstar bank at 48V is already a pretty capable buffer — using the Leaf as secondary storage introduces round-trip losses stacked on top of each other (AC→DC→battery→DC→AC if you're going the V2H route), and CHAdeMO V2H kit in the UK is still eye-wateringly expensive for what it does.

In my motorhome setup I've experimented with controlled AC charging as @TQ_Builds mentions — essentially using a Victron MultiPlus to manage export timing — and the parasitic losses alone made me question the economics pretty quickly.

What's your actual overnight discharge profile look like? If your 15kWh bank is genuinely undersized for your consumption, I'd argue expanding the primary bank with more Fogstar cells is cleaner than adding EV complexity into the loop.

Been following this with interest — we've got a similar setup in the Black Country, though I'm running Pylontech rather than DIY cells.

One thing worth flagging that nobody's mentioned yet: the round-trip efficiency losses stack up pretty quickly when you're cycling through the Leaf's battery as an intermediary. You're looking at maybe 85-90% each way, so you could easily be losing 20%+ of that energy just in conversion. Over a season that adds up to meaningful degradation cost on both packs.

Have you looked at simply oversizing your inverter/charger capacity and letting the Fogstar bank do the heavy lifting directly? Might be simpler than the V2H route @TQ_Builds mentioned. What's your typical overnight load looking like? That'd help figure out whether the Leaf is genuinely adding buffer capacity or just adding complexity. 🔋

@GoldenMaker the bit that's worth unpacking here is the round-trip efficiency cost. You're looking at roughly 85–92% into the Leaf's battery, then another 85–92% back out via CHAdeMO V2H — so realistically 72–85% overall. Compare that to just leaving it in your Fogstar bank at >99% standby efficiency and the maths gets uncomfortable quickly.

Where it does make sense is if your bank is already full and you'd otherwise be curtailing solar. Using the Leaf as overflow storage on genuinely surplus generation is legitimate. But deliberately cycling your Leaf overnight to "balance" a LiFePO4 bank that doesn't really need balancing that way feels like adding degradation to both systems for marginal gain.

What's your typical overnight consumption and how often is the Fogstar bank actually hitting 100% SOC before dusk?

Really interesting experiment @GoldenMaker. One thing nobody's mentioned yet — have you looked at your actual overnight load profile versus what you're losing to conversion? Up here in Cumbria my winter nights are long and loads are higher, so I found that keeping every usable kWh in the primary bank rather than round-tripping through a vehicle made more sense thermally as well as efficiency-wise. LiFePO4 doesn't love sitting at high SOC in cold weather either. That said, if you're genuinely seeing excess solar that would otherwise go nowhere, the V2H angle has merit as a last resort buffer rather than a primary balancing strategy. What does your overnight draw actually look like in kWh terms? That'd help work out whether you've genuinely got surplus worth capturing or whether tighter charge scheduling would solve it more cleanly.

Good thread this. @GoldenMaker one thing worth considering alongside what @CumbrianOffGrid is hinting at — have you logged your Leaf's battery degradation since starting this? Frequent partial cycles through CHAdeMO or even AC Level 2 do add up, and Leaf batteries famously don't have active thermal management, so if you're in a warmer spot or doing this regularly through summer you might be accelerating capacity loss faster than the balancing benefit justifies. Might be worth pulling the battery health data via LeafSpy before and after a few months of this regime. The maths could still work in your favour, just want to make sure you're not robbing Peter to pay Paul on the vehicle battery front.

@GoldenMaker the V2G angle is where this gets interesting long-term, but practically right now your Leaf isn't going to talk back to a non-CCS setup without serious faff. What is worth doing is treating the Leaf purely as a dumb load — use a Victron MPPT with a relay output to trigger charging only when your Cerbo sees SOC above, say, 85% and excess PV available. Essentially automated load-shifting without needing any bidirectional nonsense. I do something similar with a garden office heat pump. Not glamorous but it works reliably and doesn't touch your warranty.

@GoldenMaker one thing worth flagging from my own motorhome setup — thermal behaviour matters a lot when you're using a secondary battery as a buffer. The Leaf's pack has its own BMS that'll throttle charging aggressively if cell temps aren't happy, especially overnight when ambient drops. You might think you're balancing loads but the Leaf is quietly refusing amps.

Worth logging actual AC draw at the CHAdeMO/EVSE side versus what your Victron (assuming you're running one?) reports as exported. The delta will tell you a lot about how much the Leaf's BMS is interfering with your strategy.