Battery Voltage ranges

snipped-for-privacy@nosam.org wrote in news: snipped-for-privacy@4ax.com:

The numbers above are correct.

To test the battery properly:

Fully charged is about 12.65V. Anything less is not fully-charged.

See here for voltage charts and more explanation:

Excellent web pages. Printed it out.

After the headlight test above - what would the max allowable and/or expected voltage drop - assuming 70deg F in all cases? m

snipped-for-privacy@nosam.org wrote in news: snipped-for-privacy@4ax.com:

You mean voltage drop while cranking? Why does it matter? Use your dome light to determine that.

I'm sorry - perhaps I'm mistaken about something.

With the car off one insert the key - to turn on the headlight for 5 min.

Then one wait for 5 min and then measure the voltage. Are you saying - intend that must be 12.65v or greater AFTER THE 5 MIN TEST?

My 2nd question is - if the battery is good then how much should one expect the voltage to drop (FROM - TO 12.65V) - because the lights were on for 5 min? a. None b .3v c .6v d. ?

snipped-for-privacy@nosam.org wrote in news: snipped-for-privacy@4ax.com:

You don't need to insert the key, just turn the headlight switch with your hand.

Yes. But final voltage is dependent on ambient temperature, of course.

"D". Depends on where it started from and what the "surface charge" was. The point of the exercise is to remove the surface charge, which can vary.

The only thing that matters is what's left after the surface charge is gone. If you do the test and you get less than 12.65V (or whatever's appropriate for your ambient air temp, then the battery is either not being charged by the alternator, or it is defective/damaged/aged and cannot hold a charge.

Bill Darden explains all this on the Battery FAQ page I referenced earlier. Go read his FAQ question on testing the battery.