Sam Heywood wrote:
>>A voltmeter will not tell you whether a battery is good or bad. If I go
out to my car right now and use a voltmeter to read the voltage on my car
battery I will get a reading of 12 volts. Then I can turn the headlight
switch on and leave it on all night long. By morning my headlights will
no longer be shining and I will know that I have a bad battery. If I then
turn off the headlight switch and use my voltmeter again to read the battery's
voltage, I will still get a reading of 12 volts. The battery passes the
voltage test, but it will not pass a load test because it won't provide even
enough power anymore to turn on my headlights. If it can't even turn on the
headlights, then of course I know that the starter motor won't run either.
My point is simply this: A good voltage reading does not necessarily mean
that a battery is good. You have to perform a load test. A voltmeter does
not do this.
Do not try the above experiment at home unless you have some very
understanding neighbors who can help you get your car started in the morning
while you enthrall them with your amazing story about your adventure in
science.<<
Being of the curious kind, I decided to test Sam's hypothesis. Now, mind
you, in my youth I had access to a Model "A" which I quickly learned never to
park on level ground. The slightest slope was all that took to start it even
though cranking the starter until the battery failed wouldn't do a thing.
However, I decided to take a different tack. I had some batteries (AA and
AAA) that I knew were going bad and some brand new AAA batteries that I just
bought this weekend. As I understand Sam's hypothesis, the old, weak
batteries and the new batteries should each measure 1.5 volts. Using the
same voltmeter and the same setting, the old weak batteries measured 1.35
to 1.42 volts, while the new batteries measured 1.52 to 1.54 volts. A couple
of the old batteries were Duracell with the integral battery condition tester
(push the two dots and watch the yellow mark) and the integral tester did not
even start to move.
Hence, by this experiment, without angering my neighbors, the conclusion is
that bad/weak batteries will have lower voltages than new batteries.
Roger Turk
Tucson, Arizona USA
