Energy storageRebuild shelfHand tools, works as-is

Battery clip and holder

Also called 9V snap, AA holder, 18650 holder.

The 9 V snap from a smoke alarm or a dead toy, the AA box from a radio, the spring tube from a flashlight. Mechanically dull and constantly useful.

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
9 V snap	Large terminal is positive on the battery, which means the large receptacle on the snap lead is positive. Check anyway.
Springs	Flashlight springs are also decent battery contacts and decent short antennas.

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

Any prototype that should not depend on tape and hope

Leave this one when

The spring is rusted through. Corrosion does not make a reliable contact.

Buying a new one is the better idea when

A proper holder the moment the project leaves the bench.

How to tell if this one still works

Continuity through the wire, and a visual check that the plastic still grips a cell.

Tools you will want: Meter.

Words on this page

Short meanings, so the rest of the entry is readable if you are not already doing this every weekend.

continuity: A meter mode that beeps when two points are connected. It is how you map a switch: beep, then click, then see if the beep changes.

Where people actually find it

5 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
Infrared remote	Worth it	1	usually	AAA or AA bay.
Photoelectric smoke alarm	Worth it	1	usually	The 9 V snap.
Motorized toy	Worth it	1	always	The bay.
Digital kitchen scale	Bonus	1	sometimes	AAA versions.
Blood-pressure monitor	Bonus	1	usually	AAA bay.

Worth pullingInfrared remote1 · usually
In this particular machine
Springs and contacts.
Where to look
AAA or AA bay.
How to get it out
Clean them.
The condition to expect
Corroded often.
Worth pullingPhotoelectric smoke alarm1 · usually
In this particular machine
A real snap.
Where to look
The 9 V snap.
How to get it out
Take the wires.
The condition to expect
Good.
Worth pullingMotorized toy1 · always
In this particular machine
AA or a 9 V snap.
Where to look
The bay.
How to get it out
Clean corrosion.
The condition to expect
Springs rust.
Bonus, if you are already in thereDigital kitchen scale1 · sometimes
In this particular machine
A holder.
Where to look
AAA versions.
How to get it out
Clean corrosion.
The condition to expect
Corroded is common.
Bonus, if you are already in thereBlood-pressure monitor1 · usually
In this particular machine
A holder.
Where to look
AAA bay.
How to get it out
Clean it.
The condition to expect
Good.