Anyone else using old UPS batteries for small solar storage?

Been doing this for about three years now at my cabin. Grabbed a load of APC UPS units from a local recycling centre — bloke there thought I was mad but let me fill the boot for a tenner.

Most of the batteries were genuinely dead, but roughly 1 in 3 still had decent capacity left. Ran them through a proper discharge/charge cycle with my Victron SmartSharge and was genuinely surprised.

Current setup is a mishmash of sealed lead acids from about six different UPS units, wired up as a 24V bank. Does the job for lighting, a few USB points and keeping a little 12V fridge ticking over overnight. Nothing glamorous.

The caveats though:

• Capacity testing is non-negotiable — don't just assume they work
• Swelling or cracked cases, bin them immediately, no heroics
• Mixed ages in a bank is asking for trouble long-term
• They will need replacing more often than proper leisure or LiFePO4 cells

Honestly for a small shed or cabin where you're not depending on it for anything critical, it's hard to argue with nearly-free storage. I've probably saved myself a few hundred quid vs buying new AGMs, though I won't pretend it's not a faff.

Thinking of swapping the whole lot for a Fogstar Drift eventually, but where's the fun in that.

Anyone else pulling these from skips or recycling centres? Curious what capacity people are actually seeing on the survivors.

@Curly38 the recycling centre bloke thought you were mad — meanwhile I've got a narrowboat running partly on batteries that previously kept a Tesco warehouse's servers alive.

@Curly38 Three years ago I did almost exactly this on the narrowboat. Pulled about a dozen UPS units from a skip behind an office block that was being refurbished — bloke in the hi-vis gave me a funny look but didn't stop me.

The story nobody tells you is the sorting process. I capacity-tested every single cell individually before trusting any of them for actual storage. Probably half went straight back to recycling. The survivors formed a decent little bank that ran my 12V lighting circuit for about eighteen months before I bothered upgrading to proper Fogstar cells.

Worth doing? Absolutely, if you treat it like a project rather than a plug-and-play solution. The moment you assume they're all identical just because they came from the same UPS model, you'll regret it.

@Curly38 Really curious how you're handling the capacity testing side of things — are you just doing a timed discharge to work out what's actually left in each one, or have you got something like a battery analyser running them through cycles?

I've been tempted to do something similar for my motorhome as a cheap secondary bank, but I'd want to know the actual usable Ah before trusting them. Do the cells tend to fail individually or does the whole UPS pack usually go together?

Also wondering what voltage most of the APC units run at internally — 12V nominal, or are you reconfiguring them? That would make a big difference for how easily they drop into a standard Victron setup.

Done similar on the narrowboat. Half those UPS batteries are dead on arrival — don't bother with anything that won't hold a surface charge within 10 minutes of a quick charge. Bin it and move on.

@WattLiz the timed discharge method is fine but I use a basic capacity tester off eBay, costs about £15. Tells you actual Ah remaining. Anything below 60% of rated capacity goes straight in the recycling bin — not worth the hassle of monitoring a weak cell dragging the rest down.

Biggest headache isn't the batteries, it's that most UPS units run 12V at oddball voltages internally. Check before you assume they'll play nice with a Victron MPPT or similar — had one batch that needed a separate charge profile fiddled in manually.