Anyone else using old UPS batteries for small solar storage or is it just me?

Been doing this for about a year now on my van build and honestly can't believe more people don't talk about it. Picked up four 12V 9Ah sealed lead acid units from a local IT firm that was chucking out a load of old rack-mounted UPS gear. Paid £20 for the lot.

Tested them with a cheap capacity tester and three of the four were still holding around 70-75% of rated capacity. Wired them up as a small 12V bank for lighting and a USB charging setup — nothing fancy, just a basic Renogy 100W panel and a PWM controller I already had kicking about.

Obviously SLA isn't lithium, so I'm not pushing them hard or discharging below 50%. They're purely for low-draw stuff overnight. Wouldn't trust them for anything critical, but for a secondary bank in a van they've been absolutely fine.

A few things I'd flag for anyone thinking about it:

• Test every cell/unit individually before assuming the batch is usable
• They won't last forever — I'm treating these as a stopgap while I save up for a proper Fogstar Drift lithium setup
• Check the date codes, anything over 4-5 years old is probably not worth the effort
• SLA off-gassing is worth thinking about if you're using them in an enclosed space

Has anyone tried this with larger UPS units — the big 24V or 48V tower systems? Curious whether the batteries from those are worth salvaging or if the capacity degradation tends to be worse at that scale. Also wondering if anyone's had issues with charger compatibility when mixing slightly mismatched units in a bank.

@DownsDweller interesting thread! I've been eyeing up something similar for my shepherd's hut build where I don't need massive capacity.

Quick question though — how do you actually test the condition of the batteries before committing to a full setup? Presumably some of those IT firm cast-offs are more knackered than others?

I've got a basic battery analyser but I'm not sure it's up to properly load-testing sealed lead acid. Did you do anything systematic or was it more trial and error?

Also curious whether you're running them in series, parallel, or a mix — and whether a standard Victron MPPT handles the charging profiles okay without any fuss?

@DownsDweller mate the IT recycling pipeline is genuinely the most underrated hustle in off-grid — I've pulled enough free SLA batteries from skip-adjacent situations to power a small moon 🌙

Worth checking the actual capacity with a proper load tester before you trust them though, because "9Ah" on a battery that's been floating on a UPS for four years is doing some creative maths if you know what I mean.

My garden office ran on rescued UPS batteries for ages before I eventually caved and went proper LiFePO4 (Fogstar cells, obviously) — the SLAs weren't terrible but the weight-to-capacity ratio made me feel personally attacked every time I moved one.

@CamperClive for a shepherd's hut it's honestly ideal — low draw, rarely moved, who cares if it weighs a ton!

@DownsDweller my garden office runs on a frankenstein rack of salvaged UPS batteries wired in parallel and honestly the Victron BMV-712 watching over them looks more stressed than I do.

@DownsDweller ran almost exactly this setup in my first van build — four 9Ah SLAs from a scrapped rack UPS, wired to a cheap PWM controller. Worked, but taught me some hard lessons.

The capacity testing step is non-negotiable. I skipped it once, assumed all four units were roughly equal, and ended up with one dud dragging the whole bank down within six months. Now I load-test every single cell before it goes anywhere near my bus bars.

Also worth watching the temperature. Van environments in winter will absolutely hammer already-tired SLA chemistry. I use a basic battery monitor (started with a cheap Votronic clone) to keep an eye on real-world capacity versus what I think I've got.

For @CamperClive's shepherd's hut — static installation makes this much easier to manage than a moving vehicle. Should work well if you test first.

@GlenSimon "frankenstein rack" is doing a lot of heavy lifting there and I respect it enormously.

My cabin setup started the same way — grabbed a load of APC UPS batteries from a data centre clearout, stuck a Victron BMV on it to watch them die in real time, and now I'm three years in and somehow still going. The trick nobody mentions is testing internal resistance before you bother wiring anything — half those batteries are cooked before they leave the building and you won't know until your lights flicker at 8pm on a Sunday. Cheap conductance tester off eBay saved me more grief than I care to admit.