Dual Battery Problems

sahls01gmc · January 23, 2008

I have an 01 SIERRA 2500LD 4x4. I'm not sure if it has the dual battery standard, or the previous owner added it or not. For some reason, the additional battery does not recharge like the main battery does. I had a stereo amp hooked up to the additional battery after i replaced them, and after only a couple of days, my amp started cutting out because of "low voltage". When i took a volt-meter to it, it was only reading 9 volts when the motor was running and when it wasn't.

This makes me believe that it is not hooked up correctly. From a no brainer's standpoint, it would seem that all it needs is are leads connecting it to "ground" as well as to a load source. Does anyone have a wiring diagram for factory dual batteries, or know where I can find one?

Thanks for any help or suggestions

James

masterp2 · January 23, 2008

It is a simple system. Each battery should be run to a commom block. If you are only seeing 9 volts when running, and the other one is seeing 13-14, then the battery could be bad. Each alt should also be run to the common block, for redundancy.

If you have one alt charging one battery, it was done incorrectly. If this is the case, that alt may be bad.

Boomer73 · January 23, 2008

I have an 01 SIERRA 2500LD 4x4. I'm not sure if it has the dual battery standard, or the previous owner added it or not. For some reason, the additional battery does not recharge like the main battery does. I had a stereo amp hooked up to the additional battery after i replaced them, and after only a couple of days, my amp started cutting out because of "low voltage". When i took a volt-meter to it, it was only reading 9 volts when the motor was running and when it wasn't.

This makes me believe that it is not hooked up correctly. From a no brainer's standpoint, it would seem that all it needs is are leads connecting it to "ground" as well as to a load source. Does anyone have a wiring diagram for factory dual batteries, or know where I can find one?

Thanks for any help or suggestions

James

There is a good bit of information on this site regarding the dual battery setup - both factory and aftermarket options. A little searching should yield all the information you need. In brief, I believe that regardless of whether or not the batteries are factory or aftermarket, they should be connected in parallel. The main battery (driver's side) should be connected as in any other vehicle. The second battery (passenger side underneath the fender brace is factory position) should have the positive side connected to the main battery positive, and the negative side connected to ground (on the chassis). There may also be a battery isolator in line with the second battery to prevent the second battery from draining the primary battery in the event of a fault. If it doesn't, it should still work, but probably is a bad idea. These trucks come with alternators with output suited to charging two batteries when they are functioning normally.

It's possible that everything is hooked up properly and you just have an open cell or something in the second battery. Have you tried disconnecting the second battery and see if it will take a full charge from a standard workshop charger? I got a Husky brand charger from Home Depot a while ago for cheap that will list all kinds of errors when you hook it up to charge. Saved me money guessing more than once.

sahls01gmc · January 23, 2008

There is a good bit of information on this site regarding the dual battery setup - both factory and aftermarket options. A little searching should yield all the information you need. In brief, I believe that regardless of whether or not the batteries are factory or aftermarket, they should be connected in parallel. The main battery (driver's side) should be connected as in any other vehicle. The second battery (passenger side underneath the fender brace is factory position) should have the positive side connected to the main battery positive, and the negative side connected to ground (on the chassis). There may also be a battery isolator in line with the second battery to prevent the second battery from draining the primary battery in the event of a fault. If it doesn't, it should still work, but probably is a bad idea. These trucks come with alternators with output suited to charging two batteries when they are functioning normally.

It's possible that everything is hooked up properly and you just have an open cell or something in the second battery. Have you tried disconnecting the second battery and see if it will take a full charge from a standard workshop charger? I got a Husky brand charger from Home Depot a while ago for cheap that will list all kinds of errors when you hook it up to charge. Saved me money guessing more than once.

I have not tried to charge the second battery, but i know that the previous battery had the same affect. I replaced both batteries at the same time, since the primary was going dead i figured it was a good idea to start fresh with 2 new ones. I will try throwing the second battery on the charger, and see if it holds. Also, I will have to check the wiring.

So, according to what you're saying, there should be a wire going from the positive lead on the second battery, and then directly to the positive on the primary battery (with or without the isolater)? And then the negative cable goes to chassis ground? Then the secondary will receive it's "charging" from being hooked up to the main battery's positive cable? There is no other wire that goes from the alternator to the secondary battery?

I will search around a bit, and stick my head under the hood and try to figure it out.

Thanks for the help

James

Boomer73 · January 23, 2008

I have not tried to charge the second battery, but i know that the previous battery had the same affect. I replaced both batteries at the same time, since the primary was going dead i figured it was a good idea to start fresh with 2 new ones. I will try throwing the second battery on the charger, and see if it holds. Also, I will have to check the wiring.

So, according to what you're saying, there should be a wire going from the positive lead on the second battery, and then directly to the positive on the primary battery (with or without the isolater)? And then the negative cable goes to chassis ground? Then the secondary will receive it's "charging" from being hooked up to the main battery's positive cable? There is no other wire that goes from the alternator to the secondary battery?

I will search around a bit, and stick my head under the hood and try to figure it out.

Thanks for the help

James

Yes, there should be a heavy wire - like 2 AWG or something - going from the positive lead on the primary to the positive on the secondary there may also be a fuse. If there is an isolator it will/should be between the two batteries on the positive lead. The setup will work fine connected in parallel if there is no isolator. The purpose of the isolate is to prevent a fault in the secondary battery from draining the primary battery. A fault here could be anything "open" - an open cell, an accessory constantly on, a short etc. To clarify, there should also be a lead going from negative on the second battery to negative on the primary battery or to ground.

Think of the system in terms of water where Volts are pressure and Amps are flow/current. When the two batteries are connected in parallel you have one "super battery" with the same pressure (12 Volts) but twice the current capacity. So when the alternator is charging, it is essentially charging one big battery. It charges through the first battery (think of it as a reservoir) and this charge "flows over" into the second battery. If there is a hole/leak in the second reservoir, the "flow over" will drain the first battery. The isolator prevents this from happening. If you have no hole/drain in your second battery, then this is not an issue. Think of the isolator like a smart valve that says "ah, there's a leak in the second reservoir, the first reservoir is my priority, therefore I will shut off flow to the second reservoir until the first is full."

I think you need to determine first if the wires are connected properly and whether or not you have an isolator or some such device inline with the batteries.

Situation #1: If there is no isolator, and the wiring is correct, then a drain in the second battery should produce a drain in the first battery.

Situation #2: If there is an isolator, the wiring is correct, both batteries are new and matched, and the first is holding its charge, then I would say there is a fault somewhere in your system that is causing a drain on the second battery when the alternator is not charging.

There are probably some other possibilities including the presence of a voltage regulator that is malfunctioning but without knowing what all is in there its hard to say. You need to identify all the parts in the twin battery system. You might also check your alternator to make sure it is functioning normally and has the proper idle and at-speed output.

builderpaul · January 23, 2008

GM has 2 dual battery options.

One is direct parallel connection. This is used in all duramax. It is available on all other pickups. It is the preferred hookup for people that plow and need lots of power for short times.

The other option is more popular. It is the isolated option. This is preferred by people that use power with the engine off. Parked trailer use, inverters, big sound systems. etc. The isolated system allows the second battery to be totally discharged without drawing off the main battery. When the alternator puts out current the isolator is bypassed and both batteries charge. Sounds like there is a fault in your isolator circuit. If you don't need the isolator system converting to parallel is easy and cheap.

RPO code TP2 is the direct parallel connect

RPO code 8BO is the isolated hookup

renolaw · January 28, 2008

i'm in the process of wiring up the 2ed battery, located in OEM aux location. have 1 ga welding wire, lugs and crinmping tool, so that part is easy. will go with a simple parallel set up, running two cables from hot to hot and neg to neg. am considering some sort of continuous duty rated solenoid to 'isolate' the batteries, but am still out on how to energize the solenoid. a switched 12 volt source is one way, using the ignition to power the solenoid or like on my jeep, go with a manually selected solenoid, with a switch on the dash. hummm...

found a great place to pass wires thru the firewall-- lower left where the ebrake cable passes thru is a good spot to drill a hole, then i enlarged it w/ a die grinder. add a grommet and its good to go!

So any opinions of ignition based solenoid switching versus a manual switch? i am leaning toward the manual, so that i can turn the charge/discharge circuit on/off manually rather than always on.

Need to locate a switched 12VDC source under the hood anyway to power the PIAA light relay, etc. Ideas?

tnx

mark

markw8 · January 29, 2008

My truck is a 2000 6.0 2500 with the factory dual battery setup. I think yours is wired the same. The only time the aux. bat. is in use is with the key in the run position. There is a relay that connects the two. I don't know exactly how it functions, but possibly this relay is your problem. If your main bat. goes dead and the aux. is good you can use jumper cables between them to start your truck. If the main bat. still has a bit of charge you can turn the key to run for a period of time, this could possibly build the main enough to start. This last info was FWIW. Mark.

jp1977 · February 6, 2008

Both baterries are not used at all times. The driver side battery is basically a spare unless you rewire it. It is not a good system from original GM. I had the same problem.

RazorKQ · February 8, 2008

i'm in the process of wiring up the 2ed battery, located in OEM aux location. have 1 ga welding wire, lugs and crinmping tool, so that part is easy. will go with a simple parallel set up, running two cables from hot to hot and neg to neg. am considering some sort of continuous duty rated solenoid to 'isolate' the batteries, but am still out on how to energize the solenoid. a switched 12 volt source is one way, using the ignition to power the solenoid or like on my jeep, go with a manually selected solenoid, with a switch on the dash. hummm...

found a great place to pass wires thru the firewall-- lower left where the ebrake cable passes thru is a good spot to drill a hole, then i enlarged it w/ a die grinder. add a grommet and its good to go!

So any opinions of ignition based solenoid switching versus a manual switch? i am leaning toward the manual, so that i can turn the charge/discharge circuit on/off manually rather than always on.

Need to locate a switched 12VDC source under the hood anyway to power the PIAA light relay, etc. Ideas?

tnx

mark

Mark,

Check out the "Painless" brand of accessories. I put one of their battery kits on and it works great.

tedco21 · February 9, 2008

If its a factory aux battery installed, check the fuses. There is a fuse for that circut. It may be combined with something like 4x4. I had one of these that stopped charging the aux battery and the problem ended up being a missing 4x4 fuse. Someone thought that since the truck did not have 4x4, it wouldn't hurt to steal the fuse when another burnt out.

Just a thought.

smokeater785 · February 16, 2008

While we're on the subject, does anyone know any more about tha lonely little plug on the passenger-side firewall underneath the a/c accumulator? It's supposed to be the battery isolator connection but thats all i've been able to figure out thus far; where does it leed to, how do you hook it up if your did not come with the dual battery option from the factory? I've already installed a second battery but i'd like to make it as O.E.M as possible.