1989 Dually. Dual batteries?

[Mild Thunder]

My dually had dual batteries, but now only has one on the pass side. Looking at the cables that are on the drivers side that would go to the battery, they are small. Like maybe 8 or 10 gauge? Is this how they came? I'd like to go back to the dual battery setup.

It also looks as if someone replaced the cables going to the starter, and engine block (pass side) and they used really thin cables. New battery and still cranks sloooow. Plan to upgrade those too.

[VileZambonie]

You can do a voltage drop test and then a starter current draw test. I posted a how to on this. I'm not sure if Chris put it in the tech section yet or not.

[choptop]

I put 1/0 cable on my trucks. It may be overkill, but if I remember right, the last amp draw check I did showed 300-400 amps when cranking. 10 is good for around 30 amps, 8 is good for around 50 amps.Way too small for starting a motor in my opinion. I think 2awg is the smallest Id trust since its only a short duration load.

[frito-bandito]

Definitely go with thicker cables, it will make a huge improvement and save your starter in the progress, also speaking of starters, that may also be your problem.

[Mild Thunder]

I may replace the starter as well when re-doing it all. You can hear the bendix hangin up sometimes. Even when the motor gets hot, it starts the same, so im thinking main issue is the cables.
As for the battery on the driver side, the positive wire goes to a relay on the inner fender. I was wondering if its some sort of setup where that battery is used to power accessories, and the other for engine starting? I cant see how the wiring going to it is suppose to crank the engine.

[Lt.Del]

I cant see how the wiring going to it is suppose to crank the engine.

It probably was an accessory battery.  And, it was probably aftermarket-not stock.  The only dual (or tripple) battery vehicles (for starting) that I can recall seeing is bigger diesel trucks, like buses and the like.  Even a diesel pickup wouldn't need two bats for cranking.

[frito-bandito]

True, but most of the diesel trucks (1/2 3/4 1 ton) came with dual batteries.

[ctl_dog]

Just sold an 04 Duramax, if one battery goes dead, she don't start, I can tell you from experience!

My 75 C20 camper special has a 2nd battery tray on the passenger side, I was thinking of adding it, does anyone have experience with the isolators? can i run accessories off the 2nd battery and not worry about the main to start the truck with one installed?

[beastie_3]

I dont have experience, but they are very popular. Many people who have many accessories on their truck like winches, extra lights, etc use them.

[werewolfx13]

I like running dual batteries, i made a tray for my old '84 gmc for the drivers side, even with two old, mismatched batteries, (15+ years on one, 7+ on the other), I never, EVER had a problem starting the truck regardless of temp.

Isolators on the other hand, I don't care for..When I was looking into isolators for my Maxima's sound system, I found out there are pretty much two types of automatic isolators. Good ones and bad ones. The "bad" ones, are what 99% of the ones you see on most vehicles are.Big hunk of aluminum heat sink, with three bolts sticking out of the top. The "good" ones, generally start at $450, will handle up to 2000 amps in/out/charge, and have ZERO effectively measurable voltage drop. The cheap ones generally lose 1.5-2 volts, and can usually only handle a 90 amp or smaller alt. If you want an isolator on the cheap, a battery terminal switch is your best bet.

As a side note, the main reason i don't like cheap isolators is the voltage drop, and that's primarily because amps (especially the Tru amps I lust for) like full voltage. Just using the second battery for a winch, lighting, etc, a cheaper isolator would be fine for a stock alt. But, IMO, if you're going to go to all the trouble of setting up an isolator, you're better off buying a matched set of good batteries with close to or over 1000 CCA, and a decent reserve capacity, and an HO alt, preferrably 115 amps or more @ 2500 rpm.