Posted 8 November 2023

Second Hand EV as dedicated House Battery?

Anyone looked into this?

A quick look on AutoTrader shows I can get a 30kWh battery (albeit attached to a Nissan Leaf ) for around £5K.

This is a LOT of battery for the money, granted it won't have all it's original capacity. But with a two charger I could dump a load of power into it over night to use/sell the next day.

As a concept, this is a cheap way to get a lot of battery storage for not much money. Are there companies that strip out old batteries from these to sell as house batteries? Cos with the price of running/insuring EVs rocketing there's gonna be a lot of them coming on to the market?
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  1. KodaBear's avatar
    The car I assume you are looking at has about 150k miles on it. For a 30kWh LEAF that is A LOT. Unfortunately all LEAFs, but especially the 30's have really high rates of battery degradation due to the lack of active thermal management, increased energy density, and the fact that you can easily overheat the pack by rapid charging it a few times in a row.

    The fact that there is no photo of the dash in the AutoTrader listing sets off alarm bells to me, as it means you can't even take a quick glance at battery health. But I suspect it will be absolutely destroyed, with high levels of degradation and probably a few weak cells too.

    A decent example of the 24kWh model would probably be better, and cost less. That will still work as a V2G/V2H solution if you want to power your house with it.

    I would personally only recommend doing so if you want an EV to drive around in and then use the battery to power your home as an added bonus though. It's not quite as simple, cheap or easily compatible as you likely think.

    And if you want battery storage at home, you are much better buying a proper product designed for this new than recycled EV batteries as that's a potential for a huge can of worms that you really are best off not getting into.
    Roger_Irrelevant's avatar
    Author
    Cheers, good info there.

    I did look I to dedicated home solutions but the cost of batteries (I think it was about £20k for about 12kWh) meant it wasn't worth it, especially when you factor in degradation i.e. you lose that £20K in 10 years before you start working out how many kWh you can sell back per day.

    Used EV batteries would appear to be a decent way of getting a lot of kWh for cheap, even if they're 75% degraded?
  2. aLV426's avatar
    It's not the best solution as the battery pack is made up of many cells connected in series which in turn are connected in parallel. Unless you are prepared to disassemble the entire battery you will have no direct control over the battery management. Note that the battery is wired to produce high voltages as well (IIRC in the 400V range). This is due to the way the batteries are configured and it means it's not easy to interface with commercial invertors to obtain either 12V DC or 220Vac.
    A better solution is to purchase ex-submarine batteries which are rated @ 2V 920 amp-hour they are TPPL (Thin Plate Pure Lead) and are better designed for trickle charging and can be easily wired to achieve a long lasting 12V source.
    There are newer technologies such as lithium iron phosphate battery (LiFePO4) that are designed for home use. 9.5 kWh / 186 Ah Capacity can be had for under £4k with a 10 year guarantee.
    Roger_Irrelevant's avatar
    Author
    I saw a YouTube vid (I know that's not a sound basis for scientific discussion ) but the guy had used I think 9 cells (each cell was about the size of a laptop) out of 48 from a Leaf battery, I think he said each one was 7V so he'd done 3S3P to give him 21V, is that not doable. I think his was around 3.5kWh assuming 75% degraded.
  3. _stan's avatar
    There are often BEV vehicle batteries on Facebook sales/ebay. Rather than buy the whole car you can buy some of the batteries for a few hundred. You'd need a BMS (battery management system) made for them but people have created them for BEV batteries. I'd say the drawbacks are they don't like ok great as they won't be in an enclosure and you'll need to make somewhere safe for them to be wired up.

    I think the best solution is something like the Seplos Mason battery pack from Fogstar. It comes as a kit for about £2-£2.5k, you'll have to build it (pretty easy, guide videos are on YouTube) and it comes with a BMS, and it's in an enclosure. You'll need an electrician to fit a suitable inverter and isolators & wiring, maybe £1000 for that. So for £3-3.5 all in you'll have 12-15kwh of storage. Don't worry about the battery degradation, even after 3000 cycles (best part of 6 years) you'll have at least 80% battery life left, they'll last many years.

    Bear in mind it weighs something like 125kg though. And you'll want a cheap night rate to charge it up. I have octopus go, night rate of 9p, day rate of 31p ish. I use around 12kwh/day so ignoring a bit of conversion loss it'll save me about £2.70/day so payback time could be around 3 years!

    Batteries like the Seplos Mason seem to work out more cost effective than solar at this point, although solar costs are coming down again.
  5. tcf's avatar
    My plan is to eventually have our 30kwh LEAF parked on the driveway, SORNed, connected to the house by V2H, alongside our other car. Indra is currently doing a V2H trial, but there's no indication of when their hardware will be available to buy. (93k miles, has lost 2 bars of battery health)
  6. TristanDeCoonha's avatar
    Do you have the driveway or garage for the continuous dis/charging? Can't imagine a wire across the pavement will be tolerated for long.
    Also, how would it affect your home insurance, as you will have modified a potentially hazardous device and left it attached to the home?
    Fair play to you, and I hope it works, but there are negatives you need to consider
    Roger_Irrelevant's avatar
    Author
    I've got drive space yes. The car could just sit there as a battery to start, but there are ways to re-case and use the battery, certainly with solar setups, not 100% sure about just battery.
  7. googleboogle's avatar
    How do you plan to sell it ?
    Roger_Irrelevant's avatar
    Author
    Octopus (and possibly others..) buy energy back during peak periods, e.g. their Agile tariff. You just need to be able to use (store) tons at night then sell the next day.
  8. brightonpat's avatar
    18 months ago I built a battery out of 16 cells a BMS and some plywood. 14kw, cost around £2200. Haven't touched it since, just works perfectly and still reporting 100% health. I believe cells cost around the same now though haven't checked recently. Leaf battery is a big thing using lithium cobalt chemistry which is much more prone to fire than the lithium iron batteries usually used domestically.
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