Bad auxillary battery draining main battery?

[caseyc]

In the past couple weeks I've been having battery problems. My 3 year old Sears Diehard (main engine) battery was replaced with a new InterState battery. The Sears battery refused to start. But now, even my new InterState battery is having trouble starting.

My Chevron mechanic believes because the 2nd auxillary battery is going bad, this is causing the main engine battery to drain and not start the engine. There is a thick red cable connected from the main engine battery to the aux battery located underneath the van. Can mechanic simply disconnect the auxillary cable and this would no longer cause the main battery to drain?

I'm very sure the three year old 2nd aux battery is bad due to poor maintenance on my part and overtaxing it. At this point it's too much effort to replace the 2nd battery due to its location. I'm more concerned now about making sure the primary engine battery is working okay.

I've had more than my fair share of battery issues in the past few years of van dwelling, haha.

Thanks!
Casey

 

[SternWake]

If the combining /separating mechanism between your house and engine starting batteries has failed, then yes one bad battery can drain down the other easily. Even if this device is working properly, yet the house battery has a shorted cell, then much/most of the alternator output will be trying to bring the house battery up, when with only 5 functioning cells, cannot be brought up, and the engine battery will not be replenished.

I seem to remember you have a mishmash of wiring and cabling done by different people at different times and many house loads were still directly connected to engine starting battery.

The position you now find yourself in, was inevitable.

I would not want to be the one to try and troubleshoot your system and get it working properly.

If your aged and abused AGM house battery, disconnected from everything, reads 10.5v or less, it likely has a shorted cell. Attempting to recharge such a battery is unwise in the extreme. An AGM battery with a shorted cell, still receiving 13.8v+ volts from the charging system can go into thermal runaway, and the result will not be pretty.

I would recommend disconnecting the house battery cables, and having the engine starting battery fully recharged ASAP.

As far as restoring function to your house battery system, I fear you need to go back to the places who wired it in the first place, and expect the 5 fingered prostate exam from them, again.

 

[Optimistic Paranoid]

Yes, a mechanic can disconnect the auxilliary cable and leave it in place for future use.  It should be unhooked from BOTH batteries.  If it's only unhooked from one, it is still energized by the other one, and will short it out if the unhooked end touches ground.

Regards
John

 

[cdiggy]

I fear you need to go back to the places who wired it in the first place, and expect the 5 fingered prostate exam from them, again.

Lmao. Funniest stuff I heard all week.

 

[Canine]

Maybe you could check the house battery with a battery tester and unhook it if it's bad.Most parts places will test it for you for free.

 

[ccbreder]

You already know the house battery is bad. Disconnect it from every thing. Better to have no house battery than to be stranded with no starter.

 

[highdesertranger]

x2 what everyone here said. your chevron mechanic should have been able to tell you what was up. they should be able to tell you if the aux battery is bad. if the aux battery is draining the main battery. if your alternator is up to par, etc, etc. sounds to me like they are just guessing, not good to have your mechanic guess. highdesertranger

 

[WheelEstate USA]

Hi Casey,

Yeah, I'd disconnect both ends of the house battery cable disconnected. Have both batteries charged and then have the house batt tested.

Off topic....RTR was great fun this year. Wish you'd been able to make it.
Hope you can come out next year.

 

[skyl4rk]

Check your ground wires and connectors.

 

[WheelEstate USA]

Check your ground wires and connectors.

True....corrosion can impede charging/starting.

I recently had starter issues and it turned out to be corrosion down on a starter connection.

 

[caseyc]

Hi guys,

Thanks for your input. The aux battery cable is disconnected from the main battery now. This seems to work for now. But only time will tell. Will update again.

Casey