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Picture of Simple LED AA Battery Tester
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We use a lot of rechargeable batteries at home, and I can never tell which ones work and which ones need to be recharged, and finding out is a pain because very few things run on just one battery, etc, etc.
So, I made something to test single batteries. It's crude and it's ugly, but it does exactly what I want it to, it works, and it cost me almost nothing. This one just does AAs, simply because I only had a single AA battery holder on hand and I mainly use those anyway. It can easily be adapted for different kinds of batteries, or more than one at once.
Here's how it works: You put a battery into a little battery clip, and if it works, an LED lights up. For that reason, it's going into the LED contest (*crosses fingers*).
(I made this without thinking to photograph it, so I'll recreate it with some diagrams and new photos.)
 
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Step 1: Materials

Picture of Materials
1 LED (any color)
1 NPN Transistor
1 Old AC adapter (preferably a lower voltage than the one I used)
Resistors in accordance with the voltage and current of your adapter (I used 2x 180Ω)
1 single AA batter holder (or other kinds, or more than one kind, just single battery holders)
A container of some sort (I used a flowerpot and some rubber rings)

Step 2: The Circuit

Picture of The Circuit
Because 1.5V is not enough to power an LED on its own, the whole circuit runs off of an old charger (AC adapter). The one I used provides 12V at 1A, which is a little high for this application, but it's all I had.

Step 3: Set Up and Solder

Picture of Set Up and Solder
You may want to set up the circuit on a solderless breadboard first to test it. Solder all the parts together, insulating with heat-shrink tubing. Use this diagram and the schematic for help

Step 4: Finishing Up

Picture of Finishing Up
The only thing left to do is put this thing in a container. I used an ugly old flowerpot. You can think of something more elegant.
BtheBike4 years ago
.. what is the the benefit of non-rechargeable over rechargeables ? this tester will come in handy for those stray alkaline batts I'm curious about . Then if I install a non-rechargeable with some juice left ,its only a matter of hours till its in the recycle bin for radioshacks dump.

I've been rotating the same 12 rechargeable batts for over 2 years. I highly recommend them . I have a cheap 4 port sony charger but it charges rayovac ,duracell, ...etc just fine ,AA & AAA .