|If you are anything like me, there are lots of batteries in various stages of discharge gathering dust around your home.
This is a very simple DIY battery tester that can help you figure out which battery could be used a bit more, and which one should be delivered on balistic trajectory to the recycle bin.
How it works
The simplest way to test a battery is to just check the voltage - usually everything below 90% of the nominal is considered unusable.
This test, however, is not very accurate -
some batteries might show a good voltage when left alone, but voltage might drop significantly under even a small load current.
The opposite is also true sometimes -
a rechargeable battery may look dead but may revive after a couple of recharge/discharge cycles.
The tester lets you measure the standalone battery voltage and then the same voltage but with a 10 Ohm load.
After several measurements of dead and good batteries you will have a pretty good idea what is normal and what is not.
The tester has a switch for selecting one of two voltage ranges, allowing it to test anything from 1.2V to 12V batteries.
After selecting the voltage range, connect the battery, and take a reading with or without a load.
The load is applied by pressing a button.
(In fact, I had planned for two buttons applying different loads, but it turned out that the 10 Ohm resistor works well enough and now one of the buttons sits unconnected - until I figure out what to do with it).
Go to the Schematics & Construction page for details on building the tester.