Hope you electrical guru's can help:

3 days ago I hop in the truck and she wouldn't start, batteries are drained too far. Couple hours on the charger and it's OK. Went to Advance Auto, they tested starter/alternator/induction, all is good. Key off power drain was .05 amps.

Batteries are drained the next morning. Charged them fully to 12.68 and 12.72 volts.

Next morning batteries are drained. Here are the numbers via digital multimeter and induction meter:

Voltage before charging, batteries connected = 12.64V (seems like that would be OK??).
Voltage with engine idling after charging batteries= 13.9V
Key off voltage after long drive = 12.9V
Key off power drain with one battery removed = .05A

Other notes:

1. Alternator is a rebuild installed about 3 months ago.
2. Truck voltmeter runs dead center, used to run higher when new alt was installed.
3. Have an amp hard wired to the battery, installed about 5 years ago. Connecting/disconnecting makes no change to induction meter readings, but there is a large spark when the wire is connected, even sticks to the battery terminal as if welded to it.
4. Opening door to turn on dome light will raise induction reading to .15A, then in drops back down to .05 with light still on. Seems odd to me.
5. Batteries are 1000 amp each installed 2008.

Any ideas? Tonight I will disconnect the amp to see if the batteries are still drained. Draining these batteries overnight enough for a no start situation seems like a serious power drain, far more than .05A.

 

Make sure everything is turned of and doors, glove compartment are closed. Remove a cable and hook a volt meter between the removed cable and the battery post. It should show a drain voltage. (It really should be zero).

Now start pulling fuses while eyeballing the voltmeter. When the voltage drops to zero you have just located the culprit circuit.

Common causes in the past (Good ole' days are) clock, stop lite switch & after market accessories.

Good luck.

Rog

 

.05A (50 miliamp) is an acceptable drain. If yo are sure about the amount of draw on the batteries then you should have the batteries load tested.

 

Problem solved:

After fully charging then disconnecting the batteries, one battery lost 0.04V in one hour and the other lost 1.34V, down to 11.35 volts. That battery is dead. Will replace it in the morning.

Thanks to all.

 

If you can afford to...it's best to replace both batteries at the same time.

Rog