Battery under truck bed?

[84TonkaToy]

hey all,
this mite sound like a stupid question, but im looking to do dual battries, and im jus wondering if i put one, or both under the bed, is all i need just longer battery cables? i know i shuld get a battery box also, but yea.....anything else i need to do? also, to do two battries, i just hook up the neg to neg, then the positive of the second to the frame rite? thanx for all your help

[Nolowrider]

I have a stepside and I once mounted mine under the driver side step. It was a big drain on the battery to run it that far from the starter. It would crank over slow. But, if you are running two batteries then that should not be a problem. Just hook them up in series.

I now have it back under the hood.

[ben@speedbarn]

If you mounted them under the Passanger side step it wouldn't really be much further away from the starter.

Many European cars run the batteries in the trunk so it shouldn't be a problem. Just run good large guage wire.

But why not mount both in the engine bay? Just want to do the clean look?

[ElGracho]

Originally Posted by 84TonkaToy

... i just hook up the neg to neg, then the positive of the second to the frame rite?...

If you do this, you'll see big sparks, then smoke, then probably a fire.

Why do you need dual batteries? That will determine if you should hook them up in PARALLEL (positive to positive and negative to negative) or use a battery isolator.

Unless you have a 24 volt military rig or some other special application, you should NOT hook up your batteries in series either.

[ben@speedbarn]

We ran parrallel in all of our plow trucks with no isolator. basically hook up all the normal things to the one battery and then all of the accesories should be on the other. Be sure to replace both batteries at the same time and use identical batteries.

[84TonkaToy]

i need them because i have many off road lights and an amp. rite now i can either run one or the other, if i try to run the amp and the lights, i drain it to the point of once its off, its dead. well......is there a difference if i run them in the engine compartment or under the bed? everyone iv talked to has duals under their bed so i figured there was an advantage to that.

[ElGracho]

Dual batteries won't fix this, you need an alternator that can keep up with the extra load. If the alternator can keep the single battery charged and you don't run it down when the truck isn't running, that will fix your problem.

There are many people around here running upgraded alternators who can make a recommendation. What size alternator are you running right now?

[84TonkaToy]

not sure. almost positive its the stock for for a 84 gmc sierra with a 350. i cant even run the radio for 5 minutes with the truck off before its dead. so i figured duals for my extras. how much would a high performance alternator run for?

[ben@speedbarn]

The only reason not to run the batteries under the hood is for weight balancing and to have a clean look in the engine bay. Unless you are running some major electronics in your bed keep them under the hood. For just extra lights and an amp I would run a good battery. Optima yellow top or something like that and look into a higher output alternator. One good battery is a little cheaper than 2 normal batteries and it will be much easier and probably last longer. Batteries like Optima are like deepcycle batteries but they also have cranking amps high enough to start the engine.

[ElGracho]

First off, describe this radio problem a little more. If you drive your truck for 20 miles without the amp cranked or the driving lights, will your battery still be dead running the radio for 5 minutes with it off? Then either your alternator isn't charging or your battery is bad. Get them tested.

If your truck didn't come with A/C it came with a 63 amp alternator. If it came with A/C it should have a 78 amp. You can get a 105 amp alternator that will bolt right up here: http://www.alternatorparts.com/alternators_gm.htm. If you upgrade to the 105 amp, you may want to put in a larger charge wire that goes from the back of the alternator down to the starter (or you can run it directly to the + battery terminal). The charge just over $100 for this upgraded alternator.

[1FaastC10]

as for the slow cranking problem previously mentioned, a bigger battery cable will/would have fixed this problem.

[84TonkaToy]

if i drive with the radio on and no lights....its fine. if i drive with my aux lights AND radio on for more than 10 min. it wont start on its own if i turn the truck off. yesterday i was cleaning it, and i left just the radio on. the truck was not running. 5-10 min later i could not start the truck without jumping it. im not sure if i drive a little while, then trurn it off and leave the radio going that it will die as fast, i havnt tried. one more thing...there has been a few times i will come out to leave, and the truck wont start. its just dead....nuthing. does this have to do with the alternator or the battery?

[ElGracho]

Yes.

[84TonkaToy]

k, awesome well guess ill go for a new battery and alternator instead. hey thanx alot for everyones help, especially ElGracho. i appreaciate it guys!

[piecesparts]

Look at the alternator output, Have someone do a load test on it and the battery. It sounds to me like you have (1) a bad diode in the alternator and your only putting out the minimum voltage and (2) the first item has caused you to break down your battery's capabilities also.
I am running a "Tuffstuff" alternator (140 amp with the capabilitiy to carry 85 amps at the idle speed (yes that is possible) Most standard alternators only carry 35 amps. I have only one battery and it is a 800 cold start amp unit. This supports (2) 11 inch SPAL electric fans, headlights, A/C, and a 300 watt stereo system. I have no problems with the system and it works great.

[84TonkaToy]

how much did that alternator cost you?

[piecesparts]

About $265.00 a few years ago, but it ended the problems of low voltage for good. Not some thing that the average rebuilt can do. I think a 140 amp replacement alternator is not cheap either and it still carries only 35 amps at idle. TUFFSTUFF is on the internet, they have other items also . http://www.performancechrome.com/en-us/dept_535.html.

[matthufham]

the problem is you're draining the battery at a faster rate than you're recharging it. drive longer than 10 minutes with your high output alt. and you should be prepared to use your amp and lights then, without losing so many volts that you can't start the truck later. my neighbor has a big stereo in his hummer and escalade, rich, and anytime he wants to show it off he starts the engine and lets it run for 5-10 and then turns the radio on. this saves him from draining the battery by letting it properly charge.

[bodydropped]

well heres my delimma is like urs im runnin a 85 amp alternator thats off a cop car and i got a 1000 watt amp and a red top optima and well i can pull up to a red light and idle and stereo off with a/c on and my volts start to drop until i give it gas and then it picks back up so what u think could be worng with mine?

[CHEVYE]

higher voltage alt. or maybe underdrive pulleys.

[piecesparts]

If you have put pulleys on the vehicle to lower the drive ratio, you are now sucking away the RPMs necessary to keep the alternator charging effectively. "March" makes a smaller alternator pulley for situations like that, I have one on my 95 Impala SS. GM sells a pulley for their Cadillac line that is smaller than the stock GM pulley also. Darn old Caddys had alot of electric stuff. The volts drops at low idle (stoplight), or the lights dim, that is because you are now charging at 35 amps instead of the 75, 100, or 140 amps that will be coming out of the alternator, when you accelerate the engine above about 1000 RPM. That is why you need a bigger low end amperage on your alternator. I had the same problem with the electric fans, stereo amp, headlights and A/C beeing on. Going down the road--No Problem, but come to a stop low volts. All the batteries in the world will make no difference if you can't keep them charged. The number of batteris changes the amount of reserve that you have, when it is fully charged, but it doesn't help you if you aren't charging them up. You want all of the bells and whistles---Buy the stuff to run it.

[bodydropped]

so i need a smaller pulley for it ? would that help alot more

[bodydropped]

and my mom has a 89 burb and we can sit at a redlight with the a/c on and it wont move at all thou

[piecesparts]

I can tell this going to be a long forum.......................Yeah a smaller pulley will help..................IF you are going to put out some decent volts with the alternator. If you are using more than you are generating then you will lose from the Get-Go. The smaller pulley will assist in getting the alternator turning faster sooner, and if you are not dragging the system into dry shutdown it will keep up. I am just telling you that maybe you should Upgrade the alternator to make sure that you are giving it what you need. Try the pulley first, but look at what else you could do to get the system working better also, because I am thinking that you will have to in the end. Now for a scarey point that to this story. If you choose to put the batteries under the bed you will get them away from the heat in the engine compartment (good thing). Battery capability decreases as they get warmer, cooler is good. However, you will need some serious battery cable to keep the loses from resistance down. Mnay guys that do something like this go to the local welding supply shop and get heavy welding cable to use for battery cables. The bigger the wire and the more strands the better. Current travels along the outside of a copper wire, thus more voltage available at the load (stereo, starter, fans, etc,)

[1FaastC10]

Originally Posted by CHEVYE

higher voltage alt. or maybe underdrive pulleys.

all alternators put out around the same voltage, should be around 13.5-13.6V.