Dual Battery - Truck Question

[DuneHopper]

I have a 97 PU 5.7 in a GMC.
Its setup with a isolator but when bought only had the one battery. When I bought the truck in 2012 it had this setup. I tested it and it works, but I do not have the extra battery in it.
I have two HD RV deepcells. Question can I use a deep cell as a the alternate battery off the isolator?
The truck is power nothing, Just PS/PB nothing else like windows, door locks. Its the 5thwheel puller.
Specs 100amp alternator and isolator.
I thought about a bigger alt, but then would need to upgrade the main alt to #4 wire, and the extra battery wires as they are not set to handle anything over maybe 125amp, plus replace the isolator with a heavier one. Trying to see if I ca get by with stock on hand so to speak.

Thanks

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[Kruel J]

Sure you can. But the RV DC battery may not have quite the CCA's to do the job. Since you have an isolator, neither battery should "leach" off the other. Mixing batteries isn't good when they are wired together, but in your case you should be fine.

And no I didn't stay at a Holiday Inn last night. But I did spend 3 years in automotive tech and 7 years in the RV service industry.

 

[Kruel J]

@v0lcom13sn0w do those GM isolators truly isolate the batteries from each other?

 

[DuneHopper]

Sure you can. But the RV DC battery may not have quite the CCA's to do the job. Since you have an isolator, neither battery should "leach" off the other. Mixing batteries isn't good when they are wired together, but in your case you should be fine.

And no I didn't stay at a Holiday Inn last night. But I did spend 3 years in automotive tech and 7 years in the RV service industry.

Thanks appreciate that, I have worked on Cars and trucks since I was 16 but not something I ever tackled. So I appreciate your experience, and help. Thanks @Kruel J luckily my truck came setup for a extra battery as there is a pan already there for it.

 

[DuneHopper]

@v0lcom13sn0w do those GM isolators truly isolate the batteries from each other?

Its a aftermarket Isolator, if that matters ???

 

[v0lcom13sn0w]

thats a good question. ive never had to answer that before. i think it depends how its wired. most people have the 2nd battery for their RV trailer to run off the truck when the trucks running.

i'll look at a schematic and post it on here for a better idea.

 

[BWH]

what brand is the after market isolator?

 

[HB of CJ]

Excellent Topic and thank you. True deep cycle RV or marine type lead acid batteries are NOT designed to crank engines. Starting batteries are an entirely different animal. Like already said, do you trust your isolator? Unless specifically needed for a distinct application like concurrently powering an RV or such, why limit yourself to just one undersized starting battery?

Potentially very cold weather coming up. What is the OEM set up on your engine? Two, (2) cranking batteries? They did that for several reasons. Availability. Weight distribution, expense. When it comes times for new cables think about going to a larger gage. It might be best if your ran two, (2) cranking batteries and a third, (3) dedicated RV battery back at the trailer? Dunno.

 

[v0lcom13sn0w]

well, i looked at a 5.7 schematic and i dont see an aux battery set up from the factory

 

[cigars]

@v0lcom13sn0w do those GM isolators truly isolate the batteries from each other?

I have an ex-police Tahoe with factory dual batteries set up. It works quite well. Lots of good info on it here... Search Results for Query: dual battery set up | Chevy Tahoe Forum | GMC Yukon Forum | Tahoe Z71 | Cadillac Escalade - Tahoe Yukon Forum

 

[Mikej]

I would check with these folks. Battery Management Panels - Blue Sea Systems

What you're asking about is pretty common in marine applications I believe. Charging/maintaining TWO types of batteries, Starting/cycling batteries. As mentioned above. Two different animals. Starting batteries are made with many thin lead plates to provide huge amperage for a short time, starting. Cycling batteries are made with fewer, thicker plates to provide a lower amperage for a longer period. Cycling batteries can be ruined by using a charger that doesn't supply the higher amps/voltage that they require. An automotive alternator should provide enough of both. You just need the system (Blue Sea?) that would keep tabs on charging needs of two different type batteries. And BTW, that deep cycle will provide enough for starting, in a pinch. I wouldn't make a habit of it though.

 

[DuneHopper]

what brand is the after market isolator?

I will have to look at it today and see for sure.

well, i looked at a 5.7 schematic and i dont see an aux battery set up from the factory

It actually has a built in battery bay on the right side, it was a factory thing as its part of the front framing under the hood.
Being this has an after market setup on it now, I can not tell if there was an original setup, other then the battery bay.

I would check with these folks. Battery Management Panels - Blue Sea Systems

What you're asking about is pretty common in marine applications I believe. Charging/maintaining TWO types of batteries, Starting/cycling batteries. As mentioned above. Two different animals. Starting batteries are made with many thin lead plates to provide huge amperage for a short time, starting. Cycling batteries are made with fewer, thicker plates to provide a lower amperage for a longer period. Cycling batteries can be ruined by using a charger that doesn't supply the higher amps/voltage that they require. An automotive alternator should provide enough of both. You just need the system (Blue Sea?) that would keep tabs on charging needs of two different type batteries. And BTW, that deep cycle will provide enough for starting, in a pinch. I wouldn't make a habit of it though.

I am going to dig in a little deeper on the wiring today, looks like some is addon some isn't I will try and post a couple pics later this afternoon.

 

[DuneHopper]

OK here is a photo of the isolator, and the extra battery bay.
There is a looks like number #6 gauge wire going across the radiator and connects to a fuse block terminal.
There are two large +battery cables coming off the main battery, one looks like the starter cable and the other goes to that block,
the wire off the Alternator appears to go to the idolator where what looks like #8 wires going to the AuX-battery
and ones goes to the main battery.
So it doesn't appear the aux works as a crank battery because the wires are not near heavy enough.

FYI, this all came about because the Alternaton is weak, and whines like a blower at times so I am replacing it
and thought well with winter coming best make sure this is all working right.

Other Notes: I added the trailer brakes,5thwheel reciever, and electronics to the system and the isolator was there prior, so not sure what the aux battery does if not work as a cranking battery.

 

[Mikej]

I'm not much of a wiring guy, especially when it comes to charging circuits, multiple batteries etc. But the unit you have appears to be what you need, to do what you want. I would think that unit would recognize the needs of starting battery and cycling battery at the same time.

"Call the man" EATON's Sure Power 9523A Multi Battery Isolator | Waytek

 

[Ura-Ki]

SO, these G.M. Trucks came factory set up for dual batteries because of the Diesel engine option, but unless it's a diesel truck, the second battery isn't used. As far as I know, G.M never installed an isolater, so what you have is an aftermarket unit! Normally your batteries need to match to crank a diesel, but in this case, you can use two different batteries as long as they can both crank the engine on their own! Find a local truck shop and get a couple of deep cycle cranking batteries, but DO NOT go over 900 CCA, those batteries are made for standby like on lift gates or reefer units, and will not last more then 2 years as a main battery! Deka and Interstate are the best brands and you can get them replaced any where in the states!
BiMart is also a great place to get batteries, but you wanna call ahead as not all stores carry the same stock!
I would also convert to top post batteries and get away from those Chit G.M. side posts and convert your cables while your in there! Use the heaviest cables you can find, usually 0/4 gau is what gets used in these applications!

 

[v0lcom13sn0w]

SO, these G.M. Trucks came factory set up for dual batteries because of the Diesel engine option, but unless it's a diesel truck, the second battery isn't used. As far as I know, G.M never installed an isolater, so what you have is an aftermarket unit! Normally your batteries need to match to crank a diesel, but in this case, you can use two different batteries as long as they can both crank the engine on their own! Find a local truck shop and get a couple of deep cycle cranking batteries, but DO NOT go over 900 CCA, those batteries are made for standby like on lift gates or reefer units, and will not last more then 2 years as a main battery! Deka and Interstate are the best brands and you can get them replaced any where in the states!
BiMart is also a great place to get batteries, but you wanna call ahead as not all stores carry the same stock!
I would also convert to top post batteries and get away from those Chit G.M. side posts and convert your cables while your in there! Use the heaviest cables you can find, usually 0/4 gau is what gets used in these applications!

the only 2 battery set up ive seen in that vintage of GM truck has been on a diesel. id be happy to post up a diesel wiring diagram to show you how the 2 batteries are hooked up in series

 

[Ura-Ki]

My brother has a 88 Chevy with the 454 and dual batteries factory. But as far as I know all the trucks that have the diesel option have the dual trays. IDK, I'm not a G.M. mechanic!

 

[DuneHopper]

The only part that has me kinda stumped is the battery wire going to the fuseblock terminal from the battery, it looks original, and there is post extension on the battery to allow two cables. Of course that could be added, but why the two + hook up to what looks original has me puzzled. I know wiring pretty well, but as mentioned never had any experience in dual batteries. Even when I drove trucks I never dealt with them, that was the shops responsibility. Yes if anyone has any diagrams that would be great. I may write the isolator manufacture and see what they have on this part too.

Appreciate all the help

 

[Ura-Ki]

Not sure here, but strait battery power to the fuse box might be for factory wired trailer brakes! Normally it should be a separate circuit and/or to a power stage, but IDK what G.M. has going on here! I'm sure @v0lcome13sn0w would have the answers.

 

[DuneHopper]

Not sure here, but strait battery power to the fuse box might be for factory wired trailer brakes! Normally it should be a separate circuit and/or to a power stage, but IDK what G.M. has going on here! I'm sure @v0lcome13sn0w would have the answers.

The brakes are wired there too but a separate post, next to it. I cant recall if it had them when I got it. As two months after I got it, I had some fancy digital programmed thing put in that works great.
They truck is odd anyone, it has a transmission brake and a few other odds Ive not seen. My Father in law has the exact truck in 96, and not the Vortec FI like I do, but also he doesn't have some items I do on the truck. Yet his has power windows and doors LOL. Hell I don't know. LOL