🚀 go-pugleaf

>Can anyone provide me with or point me to construction details for a battery
>tester?

Basically, you want to apply a load to the cell under test, then read the
voltage across the cell.  The amount of load you want to use may vary,
depending on the type of cell and the intended application.

For N cells and larger (1.5v) a good bet is to place a 10 ohm resistor
across the cell for a load, then look for at least 1.2v across the cell. 
For a 9v battery perhaps 68 ohms / 8 volts.  Little button cells for watches
etc. would be different; try 27 (or even 47) ohms and 1.1 volts.  (Things
that use button cells typically present a lighter load and have a better
tolerance for low voltage.)  A really top-notch tester would have a
different load and pass/fail scale for each cell type.

How to mechanically attach to the test cell, and how to display the results,
are up to you.

-----------------------------------------------------
Gordon S. Hlavenka            cgordon@vpnet.chi.il.us
Disclaimer:                Yeah, I said it.  So what?