Battery not charging

[erik79]

what are some reasons why a battery wouldn't charge beside it being dead...and how do you know it is dead and can't be recharged?

[FloridaKat]

Use a multimeter and check the voltage.

[tzortn]

I would bring the battery to an auto parts store that can test it for you. Around here Autozone will tell you if the battery is just weak or if it is too cooked to take a charge.

[md86]

Yup , do BOTH .
If your alternator is done , that'd be a good reason it ain't charging . Or wire messed-up somewhere (unplugged or frayed) .

[The CyberPoet]

Here's the battery test:

Disconnect the battery and charge fully (as much charging as it'll take).
Now measure voltage between the poles. Voltage should be at or above 12.7 volts. Wait 12 hours without reconnecting it to anything, then remeasure. Voltage should be exactly the same as it was before or marginally higher.

If the voltage doesn't hit 12.7 volts, battery is toast.
If the voltage drops during that 12 hour period (even 1/10th of a volt), battery is toast.

Charging system test is just as simple -- at idle, the voltage going to a new (healthy) battery needs to be at least 13 volts, and at 5k RPM in neutral it should be between 13.2 and 14.7 volts -- higher or lower than that with a known-good battery and the charging system is defective (usually the rectifier pack on the alternator).

Cheers,
=-= The CyberPoet