Anyone else using a second-hand EV battery pack as a home backup unit? Curious about BMS options

I've been down a bit of a rabbit hole lately looking at repurposed Nissan Leaf gen 2 battery modules for a home backup setup. The appeal is obvious — you can pick up a 24kWh pack off eBay or from a breaker for £800–£1,200 depending on degradation, which is extraordinary value compared to purpose-built LiFePO4 banks. I've got a 4kW solar array on the roof already feeding a Victron Multiplus-II 5000, so the infrastructure is mostly there.

The bit I'm stuck on is the BMS situation. The Leaf modules don't have an onboard BMS you can just wire up and talk to — you either roll your own using something like the Orion BMS Jr, faff about with an open-source option like DALY or JK, or try to interface with the original Nissan BMS which apparently needs a fair bit of CAN bus wizardry to get working properly. I've seen a few builds on the DIY EV forums but most of them are US-focused and the specifics don't always translate.

Has anyone on here actually done this with a Victron system specifically? I want to know if you managed to get proper DVCC communication working so the Multiplus plays nicely with the BMS rather than just relying on voltage limits. Also curious what degradation level you'd consider a hard no — I've seen packs advertised at 80% SoH but I'm sceptical some of those figures are accurate.

DH_VanLife | 847 posts

@AlanWilson great timing on this thread — I've got a salvaged Leaf gen 2 pack running in my van conversion and recently helped a mate set up a similar static home unit.

One thing worth flagging that doesn't get mentioned enough: those Leaf modules run at a nominal 7.6V per module, so your BMS selection really needs to account for that unusual cell grouping rather than assuming standard lithium profiles.

We ended up using a Batrium WatchMon for his setup — pricier than the Chinese alternatives but the UK support and proper documentation made it worthwhile when we hit configuration issues.

Also strongly recommend getting the pack capacity tested before committing to a BMS purchase, as degraded cells can seriously skew your sizing decisions. What's your target usable capacity?

WildMechanic | 1,203 posts

@AlanWilson solid project choice — Leaf gen 2 modules are genuinely one of the better options for this right now. One thing worth flagging that I don't see mentioned enough: the original Leaf BMS won't talk nicely to most inverter/charger combos you'd want to use at home. Most people I've seen do this successfully have swapped to a third-party BMS — the Batrium Watchmon is popular, as is the JK BMS for tighter budgets.

Also worth checking individual module voltages before you commit to a full pack purchase. Breakers yards don't always store these properly and you can end up with badly imbalanced cells. A decent spot-check with a multimeter before handing over cash saves a lot of headaches later. What inverter are you planning to pair it with?

ExJoiner19 | 134 posts

Watching this thread closely — I've been pricing up something similar for my garden office build. One thing I keep hitting a wall on is the cell balancing situation with these repurposed modules. When you're pulling them from a pack that's already seen 60-80k miles, are the individual modules reasonably matched still, or are you spending ages with a cell log sorting the duff ones?

Also curious whether anyone's successfully paired one of these with a Victron MultiPlus without it throwing fits over the non-standard BMS comms. I know Victron plays nicely with certain protocols but I'm not sure where repurposed Leaf modules land on that.

@DH_VanLife did you go with an off-the-shelf BMS or something custom? The JK BMS units seem popular but I've not seen many people using them specifically with Leaf chemistry.

JakeHall76 | 412 posts

@AlanWilson I've been running a similar setup for about 18 months now — grabbed four Leaf gen 2 modules from a breaker up in Yorkshire. The BMS question is the critical bit honestly. I went with a Batrium WatchMon after a lot of deliberation and it's been rock solid, though it's not cheap. Worth every penny for the cell-level monitoring alone.

One thing nobody mentioned yet — definitely get a capacity test done on the modules before you commit to any BMS sizing. Degraded cells can behave unpredictably under load and you want accurate figures before you start designing around assumed capacity. Some of those "24kWh packs" on eBay are realistically delivering considerably less.

@ExJoiner19 garden office use is actually a brilliant application for this — lower peak demand makes the whole system much more manageable.

IvyLes | 287 posts

Not Leaf modules but I've got a similar frankenbattery situation on my narrowboat — repurposed EV pouch cells with a Daly BMS which has been... fine? Not glamorous but it works.

One thing worth flagging for a home setup specifically — check your home insurance situation before you go too deep. Some insurers get twitchy about non-certified battery installs. Might be nothing, might be a headache if you ever need to claim.

Also @JakeHall76 curious what you're using for monitoring? I keep eyeing up a Victron Cerbo just to get proper visibility on state of health over time, feels like flying blind otherwise with second-life cells.

The degradation unpredictability is the bit that'd keep me up at night for a static home backup vs my boat where I can just keep an eye on it daily anyway.