Battery tender/maintainer on M1009 with 12 volt conversion?

[ReubenJames]

I have a 1985 M1009 that has had the Roscoe Common 12 volt conversion done and would like to hook up a NAPA battery tender/maintainer that I have but have few questions. I searched this forum and did not locate the answer since most of the vehicles mentioned are still 24 volt. I checked some other forums (Diesel Place, etc) and it seems it can be done by hooking the positive from the maintainer to the positive on the front battery and the negative from the maintainer to the negative on the rear battery. The concern that I have is that both my negative terminals on my battery are not directly connected. The front battery negative goes to the frame above the headlight and the rear battery negative goes to the ground block on the firewall. Does any one know if it will still work in this configuration or do I need to run a jumper from the front battery negative to the rear battery negative. I know that most vehicles here are 24 volt but thought maybe someone might understand electrical issues better than I do and point me in the right direction. Also can I do away with the front battery negative that is attached to the frame and just run the cable to the negative terminal on the rear battery. Thanks for any help that anybody can give me.

 

[Cruceno]

You should really charge the batteries separately, ideally with separate maintainers/chargers. If you only attach the one charger to your two batteries, you'll only be getting half of the advertised "charge" to each battery.

Your batteries are wired in parallel to provide you with the 12 volts. I wouldn't run a jumper wire between the negatives. The truck itself is acting as the jumper, or common.

I don't see anything wrong with the setup you've described, but I would use two tenders vs one.

 

[ReubenJames]

Thanks...I would have bought a dual one for two batteries if they had one but these small towns don't stock much. We are expecting some sub-zero temps the next few days and I wanted to put it on in to keep the batteries warm in case I need to drive it.

 

[steelandcanvas]

I would think most battery maintainers are designed to charge at least (2) batteries in parallel. I know for sure my Battery Minders are. If you are maintaining and not charging, I cannot see where "half the advertised charge" would be a problem.

 

[Cruceno]

... I cannot see where "half the advertised charge" would be a problem.

Not a problem necessarily, but I don't want him to hook up a battery charger intended to charge a single battery and be upset/disappointed/stuck because it didn't perform like he wanted. More of an FYI. I don't see it hurting anything. Its not like it will DIS-charge his batteries. Reuben, if that's all you've got then go ahead and use it for now. But if I were you, I'd add another one when you're able.

 

[ReubenJames]

I will just being using it to maintain the battery and keep them warm. Charging is not my concern at this time. Thanks for all the replies.