Wiring up dual batteries

[B_derK20]

I've recently parted 2 trucks. Each one had a dual battery setup. The diesel was simple with the long positive cable from battery to battery. The gas motor was more complex. The batteries were not connected to each other. The auxiliary battery had a wire running to a relay and then a wire to the distribution post on the firewall my question is assuming I get 2 fresh batteries so they don't draw each down, can the two systems be combined so I get the benefit of the extra battery for cranking as well as a way to power other accessories or are the 2 methods incompatible or otherwise a bad idea together?

Thanks!

[86c20]

so you are wanting 4 batts? seems a bit much. on my k30 i ran a feed to a new fuse box off the aux batt and a feed from my 140 alt right to the main batt. works fine. plz give more info on what you want

[tucsonjwt]

I am not sure what set up you have on the gas engine. Usually, they auxiliary battery is run to an isolator. You might want to read up on isolators to see how they work. As I recall, I once had an isolator which would charge the auilliary battery after the primary battery was charged, but I had a relay wired through a dash push button which I could manually engage if I wanted to use both batteries to start the vehicle.

[cerial]

First we need to know what year truck so we can see what kind of amperage your talking about.

If you are trying to feed multiple batteries with one 63amp alternator that puts out like 30 at idle you are going to be working that thing hard.

I get beef for running two alternators instead of isolators sometimes. But the wiring is extremely simple. Just 3 wires and you are good. The system in itself is cheaper once you factor a good isolator is going to run you at least $200.

My 84 has two 63 amps that combined at idle put out 60 amps. On my 76 I am going with twin 144 alternators and will be putting out around 160 at idle. At around 3k they will be putting out 280 which is enough to accommodate any kind of voltage sucking accessory I might want to plug in to the inverter.

What I recommend is 4 pole main cutoff switches. They isolate the batteries fully. Napa sells them for around $50. But, you can get them from cheaper for around $35 if you search around.

This is the best way I have found to truly isolate batteries. You turn the switch and the entire electrical from the switch to the truck is off. You only have the 0-2 gauge wire from the battery to the post on the switch hot any all times. This means no drain at all. I have parked trucks and equipment with these switches for 4-6 months came out turned the switch and they cranked like they had been sitting for a hour. An isolator has left me stranded 4 times on 3 different rides.

Wiring is simple. Ground wire, wire to battery (10 to 6), sensing wire(to horn relay or power block), wire to light/gauge.

You run the wire to the battery directly keeping it short. Or you can run it to the switch then to the battery to gain the one wire only hot at all times that I like.

Most vehicles have a 6-8' 4 gauge wire to the starter, 12-20' of wire to the key, another 40' or so wire to the lights/flashers. This is the minimum hot at all times wiring on a common vehicle from 1965 to 1990. That is not even going into all of the blade type connections that are known for corroding or relays or many other small electrical sucking items.

By adding a main kill switch that is fed by a main wire from the battery them running the truck off the main(switch on) post you eliminate the chance of any of that 60+ feet of hot at all times wiring causing a issue. You end up with 1 wire around 8 feet that is hot at all times. On dual batteries you need another wire around 8 feet to a second switch. On my 3 switch dual battery system (one of the switches is a jumper switch hot only when both switches are on and the third switch is on. For jumping only) I have only around 11 feet of hot at all times wire with only 4 hot post.

This means when I go up north and park the truck in -20 degree weather or out to the local event with the radio cranked or have the cooler running all night. I know that I can throw the aux switch and the truck will fire right up. It also means that in the event of a fire or accident the switch can be thrown to kill all the electrical from the switch on.

If you want to run 4 batteries you can. But unless you feel like dropping some serious coin on a fancy hard to find high amp alternator and a expensive isolator to handle the amps that that higher amp alternator is going to put out. I would go with a dual alternator setup that will keep two 1000 amp batteries fully charged at all times then a setup of 4 batteries that are only charged to 40-60%.

[andrewmp6]

2 batteries is more then enough,If you want to buy a wiring kit http://www.12voltguy.com/DUAL-BATTERY-KIT.html

[B_derK20]

No I don't need 4 batts. What I was wondering was if the auxiliary batt could be hooked up positive to positive and also like this diagram or if it had to be one way or the other but not both

[B_derK20]

I guess the simplest way to ask my question is in the image above, could you connect the positive terminals like you would on a diesel engine or would that be a bad idea. My truck is an '83 with a 350, the first truck I parted was an '84 with a 6.2 (both batteries connected) and the other truck I parted was an '82 with a 350 (2 batteries wired like the above diagram)

[Keith Seymore]

The philosophy is different.

On a diesel the two batteries are wired such that both assist with cranking.

On the gas version, RPO TP2 (aux battery) is wired such that one battery cranks and the other is held separately, in order to run 12V systems (pumps, campers or whatever) without depleting the cranking battery.

K

[andrewmp6]

A diesel needs the power to crank them over in the winter time.A gas truck only needs a 2nd battery if its a off roader with a winch and a lot of lights,Or you pull a camper/race car trailer that needs the power.

[wilkin250r]

CAN you do it, and SHOULD you do it are two different questions.

Yes, you can hook up both positives together. In electrical terms, this is "in parallel". Your alternator will charge them both, they will both crank the starter.

There are some minor problems, I would make sure to get both brand new, identical batteries. Deep-cycle batteries and cranking batteries hooked together in parallel don't give you the best of both worlds, they give you the WORST of both worlds. Different batteries, different manufacturers and different specs can easily have enough differences to cause problems (even an old and a new of the same type), but if you get two identical brand new batteries, your chances of complications are very slim. There are also a host of other concerns (like alternator amperage) that we can discuss if you want. None impossible, but need to be addressed.

But why? One good battery should easily have enough to crank your engine. If it doesn't, you don't have a battery problem, you have a starter problem.

If you're looking for more capacity, for high-drain devices (camper? Winch?), then you DON'T want both batteries tied together. You want to isolate one to use for your high drain, and save the other for starting so you won't be stranded.

To answer your questions, yes, you CAN hook up two batteries like that. But I don't see any point in it. For almost any application I can think of on a gas engine, having your two batteries isolated from each other will be better.

[BLE 'BURBAN]

Here's how i wired up my second battery.
Secondary positive to primary positive then to starter.
Primary negative to secondary negative then to ground.
This doubles my c.c.a. To 1600 instead of only having 800 with an extra large reserve capacity.
This way i'm drawing off of both batteries at the same time.
My last pair of optima batteries i had i purchased in 1999. They lasted until this past fall wen i finally had to replace them. That's 15 years, 2 trucks and one suburban later.

[BLE 'BURBAN]

Yeah it's overkill but that's what i like.

[B_derK20]

I wonder if you could have ordered RPO TP2 with a Diesel engine? If so, how do you suppose they would have wired it up? Really the only reason I was considering doing this was because I had both the extra long positive cable from the diesel truck from battery to battery and the pieces in the above diagram from the gas engine truck with option TP2. I was planning on buying 2 brand new batteries. I didn't consider how much more load on the alternator it would be to keep them charged though. What is the highest output stock alternator I could bolt in? I don't want to mess with a one wire or other setup that requires fabrication.

[Keith Seymore]

Originally Posted by B_derK20

I wonder if you could have ordered RPO TP2 with a Diesel engine?

No. RPO TP2 was not available with diesel.

K

[Keith Seymore]

Originally Posted by BLE 'BURBAN

Here's how i wired up my second battery.
Secondary positive to primary positive then to starter.
Primary negative to secondary negative then to ground.
This doubles my c.c.a. To 1600 instead of only having 800 with an extra large reserve capacity.
This way i'm drawing off of both batteries at the same time.
My last pair of optima batteries i had i purchased in 1999. They lasted until this past fall wen i finally had to replace them. That's 15 years, 2 trucks and one suburban later.

That's how I've go this one wired.

555 cu in, 13.5:1, 950 HP....cranks every time.

K

[tucsonjwt]

I set up my big block 83 like BLE Burban. I need all of the help I can get to overcome starter heat soak in the desert. It does help, but as was mentioned you need to replace both batteries at the same time. I recently installed an Hitachi starter and it also helps. The charge on the secondary battery seems to be less than on the primary battery- probably because of the extra length of battery cables to the secondary battery. Both batteries are start batteries, no deep cycle. I have never had any luck with isolators - they seem to fail after about one year - I read that good isolators cost about $150 and up.

[wilkin250r]

I'm never one to knock a solution to a problem. If you have a particular problem and a dual-battery setup is the easiest solution, run with it.

But I've rarely ever seen a problem that actually required a dual battery (Keith Seymore's 13.5:1 compression might be one of those). Most problems can either be solved with just a larger battery, better/larger/newer battery cables to reduce IR losses, or a gear-reduction starter. Unless you have all the parts on hand, I'm thinking any of these solutions would be cheaper/easier than a dual-battery parallel setup.

[reporter000001]

wow. okay.
to address you question, yes you can combine the two systems, just use system with the relays (the aux iso system) and parallel your extra batterys off each bat. so 2 main crankers, 2 aux.

But you first have to understand that the diesel setup is a 12v double amperage system. meaning its like a normal setup, but streanth of 2........the aux setup could be used to power seperately, or ASSIST in small things, like spotlights.... usually this system is switched only.... like on a camper. these would be the tv's batterys on a seperate system, so when u get drunk and wake up the next day, the mains are still charged and you can start the car and drive away, and as driving, SLOWLY recharge the dead batterys..

any aux system is generally a low amperage system, not used to crank the vehicle, i say this because most relay solenoids are intermediate loads.... they cant crank a car for 1min straight.... they will catch on fire. now im sure many will arge with me and say just use a ford or dodge remote starter solenoid and boom,done... and they are right.... but a complicated system is always prone to failure....just parallel 2 batterys and you should be good. if you do choose to do a seperate aux system, i sugest a deep cycle, heavy duty wiring, 00 or 0g wire, emergency shutoffs, and a ford solenoid, for like a bigblock 70's....with a solarcharger.

I have a summit remote battery kit, in a plastic box in the bed, 2 batterys parallel on a arco solar.........make sure yourun a alternators senor wire (if using a 3pole) close to the batterys or the batterys will get a memory and fail in 2 years......believe me...... learned the hard way...

i have run 2 65w spots, 2 55w fog, 2 55/60w headlights,full markers, heater,sterio drawing 40a max, ele engine fan drawing 15-20a max charging my phone, windshild wipers all at the same time..you name it. my fan is automatic and runsa after u turn the car off, ive let it fun with full lights for 8 hrs, noticed i forgot.... turned the key.... vroom!!!

I have jumper several cars without the need to start the motor let alone rev it up...... my system uses duralast batterys, 1 sidepost (because thats what the kit required at the time) and 1 top post rated at a combined 1600 CCA..... I HATE HATE HATE the duralast.... never again... napa all the way!!! best batterys from a local shop...... not to mention optioma