Energy storageRebuild shelfUnplug and unscrew

NiMH cell

Also called AA rechargeable, garden light cell.

The usual cell in solar garden lights and older toothbrushes and cordless phones. Garden-light cells have usually been left flat and are the reason the light died. Corded-phone packs are sometimes still good.

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.

A loose lithium cell

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.

Specification. The right-hand column is what is typical. The label on the part in your hand wins if they disagree.
What to look for	Usual figure
Voltage	1.2 V nominal, about 1.4 V hot off charge
Charge	C/10 for time is the forgiving method. Fast charge needs delta-V detection.

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

Restoring the garden light
A low-stakes battery

Leave this one when

It leaks or it will not take a charge and hold it overnight.

Buying a new one is the better idea when

New AA NiMH. This is one of the few cases where new is clearly cheaper than fussing.

How to tell if this one still works

Charge gently, rest, measure. A cell that falls to 0.8 V by morning is done.

Tools you will want: NiMH charger, Meter.

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

2 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.

Harvest at a glance
From	Call	How many	How often	Where it sits
Solar garden light	Bonus	1	always	The body.
Electric toothbrush	Bonus	1	usually	The handle.

Bonus, if you are already in thereSolar garden light1 · always
In this particular machine
AAA or a custom cylinder. Usually the failure.
Where to look
The body.
How to get it out
Replace it if you want the light back.
The condition to expect
Dead.
Bonus, if you are already in thereElectric toothbrush1 · usually
In this particular machine
Often the failure.
Where to look
The handle.
How to get it out
Replace if you are repairing.
The condition to expect
Dead.