Energy storageRebuild shelfTest and identify
Sealed lead-acid battery
Also called VRLA, 12 V 7 Ah, UPS battery.
The 12 V 7 Ah or 9 Ah block inside a small UPS, or a larger one in a bigger UPS. Very often the UPS was thrown out because this battery is already dead. Lead and acid, even when 'sealed'.
If you are new to this category
Batteries store energy. The useful ones in modern scrap are lithium cells, and they are also the ones that burn if they are crushed, overcharged, or wired together carelessly. A pack is usually thrown out because one cell in the chain is weak, not because every cell is dead. Swollen means stop.
Tape over bare metal ends as soon as a cell is loose. Charge only with a charger made for that chemistry and that number of cells in series.
The flat end is negative, the button end is positive. Nominal voltage is about 3.6 to 3.7 volts. Full, for an ordinary cell, is 4.20 volts. Below about 2.5 volts for a long time, or any swelling, means it is for recycling, not for a project. Tape the ends so a bunch of them cannot short in a drawer.
Lead solder, leaded glass, lead-acid. Older boards are tin-lead solder. CRT glass is leaded. UPS batteries are lead-acid and full of sulfuric acid.
| What to look for | Usual figure |
|---|---|
| Voltage | 12 V nominal, about 13.6–13.8 float, about 14.4 cyclic. A resting voltage under 12.0 V is a tired battery; under 10.5 V it is probably sulfated. |
| Current | They can deliver a lot for a short time. Fuse the output. |
Volts are electrical pressure, amps are how much current is flowing, and ohms are how hard the part resists that flow. A higher voltage than the part was built for is how salvage parts die on the bench. If a cell in the table says “read the stamp”, that stamp is the whole specification.
What people actually use it for
- A float-charged backup
- A 12 V source that is not lithium, if it still holds charge
Leave this one when
The case is swollen or cracked. Recycle it. Do not open the vents.
Buying a new one is the better idea when
A new SLA of the same size. The charger in the UPS may still be worth keeping even when the battery is not.
How to tell if this one still works
Resting voltage, then a known load for a known time. A battery that sags to 10 V as soon as you connect a modest lamp will not run an inverter.
Tools you will want: Meter, A lamp as a load.
Words on this page
Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.
- nominal
- The nameplate voltage, not the exact voltage at every moment. A '12 V' lead-acid battery sits around 12.6 V when full and sags under load.
Where people actually find it
1 notes, most useful first. “Leave it” means the part is in that machine and you should not take it: it is dangerous, worn out, or only useful if you already know that exact repair.
| From | Call | How many | How often | Where it sits |
|---|---|---|---|---|
| Uninterruptible power supply | Worth it | 1–2 | always | The tray. |
- In this particular machine
- 12 V, often 7 or 9 Ah. Frequently sulfated.
- Where to look
- The tray.
- How to get it out
- Load-test. Recycle if it sags immediately.
- The condition to expect
- Often the reason the unit was scrapped.