Battery charging problem

[nbkr341]

I can put in a fully charged battery, start and drive around just fine, but if I let it sit for 24 hours there is barely enough juice to crank the motor.

Does this sound like the alternator? All four of the batteries I have been using checked out ok at autozone.

[chuckster57]

To eliminate the alternator as the problem, just take a Volt/Ohm meter and with the engine running, test across the battery posts. Should see over 13 Volts.

If you get anything over 13 VDC then it's time to start looking for a "parasitic" drain.

[Diesel Dawg]

Originally Posted by nbkr341

I can put in a fully charged battery, start and drive around just fine, but if I let it sit for 24 hours there is barely enough juice to crank the motor.

Does this sound like the alternator? All four of the batteries I have been using checked out ok at autozone.

If you have freshly charged, good batteries and you run around all day long and toward the end of the day, your batteries are dead/weak, youve got an alternator problem....

What does your voltage gauge on your cluster say while engine is running? Mine is typically by the A of "NORMAL".

Even though the batteries tested just fine on a normal car battery tester, doesnt mean that they'll turn over a diesel engine just fine....

If you have charged batteries and let the truck sit for a day or 2 then the batteries are dead, your batteries are junk or you have an electrical draw somewhere. Time to start troubleshooting your electrical system at that point.

Try this......charge up your batteries and completely disconnect them and let them sit for several days. Reconnect ONLY ONE BATTERY and try to start truck. If dead or really weak, you've got a battery problem. If it fires up, disconnect that battery and try starting off ONLY the other battery. If it fires up OK, your batteries are fine. Keep in mind that both batteries are always connected and if one is junk, it will pull the charge out of the other one as well when they are connected.

If the batteries are similar vintage and you find one to be the culprit, change em both to avoid frustration in the future...

[drinkypoo]

quick alternator test.

1. if the vehicle has been run turn on the lights for a minute to remove surface charge, then wait a minute
2. check voltage at battery. a full battery is 12.6 to 12.65 volts. higher is OK, but indicates a surface charge is present.
3. start car, check voltage at battery. should be 1.5 to 2 volts maximum over the battery voltage to a maximum of 14.65 volts. Some cars have a lower maximum.
4. turn on headlights and blower motor to full, check voltage at battery. should be 1-2 volts over the battery voltage to the same max.

if it falls down at any point test for AC volts (yes, AC) across the battery, if you find more than 20mV AC or so you've probably got a diode going bad. if it just doesn't make much voltage you probably have a diode gone or something worse.

[LMJD]

The proper way to test your alternator:
Unplug the remote mounted regulator. Take a small jumper wire and jump battery current directly to the field terminal at the alt, this forces the alt to put out it's total max current. (You can easily use a paper clip from the batt hot terminal to the field terminal) If it's anywhere from 14 to 16 volts the alt is OK. After the test remove the jumper so the alt doesn't overheat. After you've tested enough of them you can tell if the alt is good just by the small drag on the engine as you touch the field terminal.
However by your original post it sounds like you've got a constant drain overnite.

[drinkypoo]

"full fielding" the alternator doesn't test the voltage regulator, obviously. It can also damage the diodes.

[LMJD]

It can also damage the diodes.

nbkr341, FYI it can't, that's been the accepted and recommended way for decades in dealerships and shops.