84 Ford F250 with a 460. The batteries are of unknown age came with the truck and don't look all that bad. I'd figure no more than 5 years old. I had them both tested (have a dealer added camper splitter/isolator package) and it appeared that one is bad. Would it be feasible that the one bad battery would drain the other battery (the good one)?

Also I can charge it up and then shut down both batteries at the splitter and then go out a few days later and it will slowly turn over. I was under the impression that the camper setup totally shutdown the electrical flow. Even though said one battery tested out good could this be the isolator wearing out?

I guess the most likely scenario is that the bad battery is killing the other good one (although they are both the same type, age, brand etc. so I suspect the other one should be replaced also. ) The thing that gets me is whether or not the isolator could be causing this issue.

 

One battery will drain another one since they are hooked up in parallel, the vltage will equalize. One m 6.9 i had a cell short out in one battery and it pull the other one down to 8 volts

 

Sweet good to know. One sexy truck you have btw! Since I am going to be running about 10 kc lights, would it be prudent to get one huge battery and a good amp alternator 200+ amp, or the alternator and two batteries so I can isolate one and have one fresh one?

 

Why thankyou sir!2 batteries will have much more reserve and cranking amps then 1.Thats why a lot of old 24v systems used 4 6volt instead of 2 12volt. The one big battery would also be alot of weight on one plastic inner fender and the 10KC lights tells me this ain't for loading groceries! its for off roading

 

Also make sure both batteries are of the same group size or else one will kill the other off. For a high output upgrade consider a 3g style 200a alternator.

 

hang on a second, if you have an isolator it is supposed to keep one battery from draining down while using accessories (such as when the truck isn't running) so that you will always have one battery to start the engine with (and will pull juice from both to start with). non isolators just hooked the batteries up in parralell (no isolator box, both batteries connected via cables. such as a factory diesel)

however, if you go to start it and it has the load from both the starter and the dead battery pulling from the one good battery, it could cause a no-start issue. I'm gonna need to do some research into isolators, as i am only relaying what i have read in catalogs and packages in the parts store, and intend on running one in my bronco. if i find something i will return.

 

from wikipedia:

"A battery isolator helps to ensure that the starting battery has sufficient power to start the engine and recharge the batteries if, for example, loads on the auxiliary battery (e.g., refrigerator or navigation lights) cause it to be drained, or if an auxiliary battery fails."

a typical isolator system,


i would say that if your setup is hooked up correctly, your isolator may have a bad diode.

 

 

You are right muscletruck. I bet the previous owner just wired them up into parallel. That is what I did on my camper special since I don't have a camper. Lots of battery power coming from my two Optimas. And yes... a bad battery will drain the good battery. Always replace both at the same time.