Dual battery issues

[bshupe]

I took both the batteries I have down to the local battery place here in town and they tested them for me. The one I know is good held over 1000CCA for a little over 10 seconds impressing even the guys at the battery store.

The second could only muster about 300CCA but they felt like it might be restorable and so I left it with them to run for 24 hours on their battery restoration system that does a series of trickle/boost charges to break free any sulfation that might be built up in the cells. I will know later today what the results of that test are. Maybe if it comes back sufficiently enough then I will just reinstall the batteries and take the ones I put in it back.

If I reinstall the old batteries, does it make any difference which one goes where front/back? Does one have to work harder than the other so that if I do have a weaker cell it will not have to face loading all the time?

Thanks for your input.

 

[Keith_J]

The back battery only sees a load during starting.

 

[Warthog]

You need the most power out of the front battery. Both are important though.

 

[GPrez]

I would put the weaker of the 2 (assuming by weaker it is still a good battery) closest to the front of the truck. The back battery is the final passage before going to the starter etc. and I would want the best one there. I have no technical backup for this decision it's just what I would do.

When I brought my M1028 home last spring it had 2 dead batteries. One of them charged up and tested fine the other was dead dead. Someone on here mentioned that they thought I should replace both batteries, so both are in sync together, but I have had zero issues and the older battery continues to charge and test fine. I did put the older one in the front battery tray.

 

[MarcusOReallyus]

The available starting current is the sum of the current provided by each of the two batteries, and it doesn't matter which one is in which position. Since they are in series, any internal resistance is in the circuit no matter what order they are in, and any current supplied has to work against that resistance. So, order doesn't matter for starting amps.

What DOES make a difference is how often, and for how long, each battery is drained. Since the rear is only used for starting, it gets used less, and is immediately recharged (if everything is working right).

The front battery would be the one subject to getting drained by lights left on, etc. So, if a battery already flaky, this is probably not the best place for it.

All of this may be moot. If all you can get out of it is 300 CCA, you probably need to replace it anyway.

 

[bshupe]

The guys at the battery shop thought it was worth a try to run it through the restoration process and it will only cost me $5-10. Well worth it to save replacement cost.

I follow you on the issue of both batteries sharing the starting load but since one is primarily responsible for the accessories and thus will be drained/charged more frequently then I would put the stronger battery there. If Im reading the previous post correctly then the weak one goes to the rear..... unless its really weak then replace.

By the way, the weak cell is likely shorted internally and if it is shorted by excess sulfation then the process they are doing will have a good shot at correcting the problem and saving the battery.

 

[cpf240]

When I had a battery going bad, it was the front one. You'd get the classic chattering of the starter solenoid so typical of a weak / dead battery. The battery failed a load test.

As a temporary fix, I swapped the batteries around, placing the weak one in the rear position. My thinking was that this would allow the good front battery to keep all the 12v stuff, like the starter relay, engaged and hopefully the two batteries combined would have enough to crank it over.

Since I had done the 12v bypass for the glow plugs, swapping the batteries around made sure the glow plugs did their job.

Anyway, it worked fine for the week or so it took for me to get new batteries. It cranked slow sometimes, but it always started! Though I'm not all to sure my starter motor appreciated it all that much...

 

[MarcusOReallyus]

The guys at the battery shop thought it was worth a try to run it through the restoration process and it will only cost me $5-10. Well worth it to save replacement cost.

Yep, for that money it's worth a shot!

 

[bshupe]

Just talked to the battery guys and they said the restore effort was able to correct the issue with holding a charge but the CCA did not recover. They said the most they could get was about 300 CCA.

I guess if it will hold a charge for a while I could use it as the two together will have more than enough CCA to start the truck.

Decisions.......

 

[MarcusOReallyus]

Toss it. Time for a new battery. That 300 CCA translates to a high internal resistance, which will stress your good battery.

 

[Skinny]

I'd rather spend the $100 up front for a new Group 31 than have to walk somewhere on a cold morning...