We all run into a situation when
batteries in our remotes, toys, keyboards/mice run out. If we don't know how to
check a battery we might throw out a perfectly fine battery (especially when we
have a pile of them somewhere in the drawer).
This electronics tip has to deal with checking common alkaline AA/AAA batteries
or AA/AAA rechargeable batteries for proper voltage with a voltmeter.
Disclaimer : some people might say that a battery should always be tested under
load but I have found that in most common household applications this is
insignificant and will not change the results of the testing too much.
Just for you, I pulled seven (7) AA cells out of a fresh pack from the store, taped them down to my desk, collected a few other things, and made these measurements:
AA Cell Open at 25 mA Calc int R, Ω #1 1.596 1.546 3.285 #2 1.601 1.551 3.285 #3 1.598 1.539 3.876 #4 1.578 1.548 1.971 #5 1.600 1.539 4.008 #6 1.598 1.526 4.730 #7 1.600 1.547 3.482
The (open/unloaded) voltage of the cell is determined by the cell's "chemistry" ... the actual chemicals and metals it's constructed from ... that undergo the chemical reaction to deliver current between the terminals when a conductor is connected there.
-- The variation in voltage among these 7 cells is about 1.44% .
-- The variation in the internal resistance of these cells ... an indication of how much current (amps) a cell can deliver ... varies over a range of almost 140% . I am surprised.
