Read the date code. If its more then 3 years old probably dead more than 4
years old defiantly dead ! automotive batteries are made from low grade
materials and usually last about 3-4 years. Standard 'garage' tester is a
bit of bent wire and a voltmeter they look for a dip voltage of >10V under
load of about 50-100A for a few seconds to indicate serviceable


Rgds Steve



-----Original Message-----
From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of
andrew kelley
Sent: 30 March 2006 05:33
To: Microcontroller discussion list - Public.
Subject: Re: [EE]: Test car battery

Hey,

> How to test the card battery when is dead? The last
> time I tested the dead battery, the pd. was 12v
> ish...... The voltage rating for the car battery. Use
> an ammeter?..... Any clues?

One of the best ways other than just charging and trying it out in the
car is to:  put it on the charger anyhow, but make sure the charger
has a amp guage, so you can see how much current the battery is
pulling.  If it doesn't start the car or even sounds like its not
trying at all, the charge guage(ammeter) on the charger should read
close to full scale, and should stay at near full charge rate for at
least 2 hours.  If the rate drops significantly within say between a
half hour and somewhere up to an hour and a half, go get a new
battery.  If not, leave it on charge overnight and then plop it in
after and try it out, and you'll find out how soon it will die again
if at all.  One other thing is to make sure the alternator is good
too.  (usually idiot lights take care of that, but not always [like on
my plym horizon])  If you have a battery guage in the car, you should
be able to watch it not drop while you drive down the highway (or
leave it running for that matter, with the lights on after its been on
for 15 minutes).

> Thanks,
> John

No problem

--
andrew

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