Battery Discharges

[hogdriver]

Low mileage 2006 LBZ. Truck starts after charging batteries overnight. However, if I fail to trickle charge overnight, the truck will not start in the morning as the batteries discharge. I've checked the voltage on both batteries and they are both below 12v in the mornings I fail to charge the batteries. This has happened in the past 10 days. I have not had a chance to take it to shop, thinking I could isolate the problem myself.


Any ideas?

[DmaxMaverick]

Any accessories plugged in or connected, even if not "in use"?

Could be failed/failing battery(ies). Try disconnecting them overnight and check the voltage in the morning. They should be the same between them, and close to what they were the night before. Certainly not below 12V. Healthy batteries should last a couple/few weeks of off time before showing any issue. If the problem isn't the battery(ies), at least you'll be able to start in the morning while continuing the diagnosis.

[JohnC]

Yeah, disconnect both batteries. One weak battery will drag the other one down with it. My guess is you'll find that [at least] one of them is self discharging over night.

[hogdriver]

I put an ammeter on the battery neg post to negative lead, when it was disconnected. It showed a current reading of about 400mA. Most vehicles read no more than 50-100mA when there are no lights on and the ignition switch is off. So there is something pulling an inordinate amount of current.


I am disconnecting the batteries tonight to see if one battery is bad.

[Kennedy]

1) How old are the batteries?

2) isolation testing is the best first step

3) You have to wait several minutes for the load to drop as the various items go to sleep after being reconnected

4) Amp hound is a neat relatively inexpensive tool to see which fused circuits are carrying current.

More than likely old, tired batteries. Even if not old, being drawn flat like this several times can really take the life out of them quickly.

[spongebob]

I have 400,000 miles on my truck and have replaced the batteries every 4 years...do them both when you have a bad battery.

[trbankii]

Also helps to swap the batteries side to side so they get a more even amount of use. I do it every fall.

[DmaxMaverick]

Also helps to swap the batteries side to side so they get a more even amount of use. I do it every fall.

If your batteries aren't getting even use, your system is broken. Swapping battery locations balances heat exposure differences, which can be significant. If you're using AGM batteries, the effect is less or not at all, depending on the actual conditions.

[trbankii]

Well, I maintain that the system is broken from the get-go with the OEM cables. I'm actually in the process of fabbing up new cables out of welding wire.

[DmaxMaverick]

Absolutely. I toss them at the first (last) indication. My 2001 hasn't had any issues, other than normal battery replacement (knock wood), but every other previous has. Welding cable is the right answer. I enclose it entirely with split-loom to give it some rigidity and protection once installed to keep it out of trouble.

[spongebob]

Hogdriver ??

[JohnC]

Hogdriver ??

MIA since 5/13

[spongebob]

MIA since 5/13

I hate it when that happens..now we’ll never know what happened.....