Good thing I'm not an electrician!

 

You're right that without a switch or an isolator, when and if one battery goes bad it will drain the other one. If both batteries are good, there is no problem running them without a switch or isolator, they will both settle at full charge and then discharge equally when a load is applied, provided the batteries are of similar size and capacity. The switch is a good idea, is easy to install, and doesn't really have any drawbacks beyond the added cost. An isolator on the other hand will mean the batteries are never fully charged unless you have a regulator with remote sensing capability, something most cars and trucks will not have.

 

Hey Gibby

Thought you might be interested...

http://www.excessiveamperage.com

 

Do both!

High power alternator install on a '85 Toy 4Runner, 140 amps for $140:

http://news.yahoo.com/news?tmpl=stor...r_050128235115


Dual battery installation:

http://www.rocketcityrockcrawlers.co...20Part%20I.pdf

Thanks,

Al

 

Here's my set-up....
https://www.yotatech.com/forums/show...dual+batteries

This computer is messed up, that should take you there....

I would put some sort of isolation device no matter what. Obviously you're not going to run them together for a 24 volt system. If you simply "hook them together" they will kill each other in a short time. I've spent years with in the stereo scene and on my way as a mechanical engineer (not electrical!) but I think I can explain why easy enough. Electricity flows from areas of higher concentration to lesser concentration. I could go into details and yadda yadda yadda, but it's a basic law of physics. When you put those 2 batteries together and they're sitting there, freely exchanging current, they really do kill each other. You can have 2 of the same battery from the same batch built on the same day, essentially THE SAME 2 batteries. BUT, one is going to have slightly more charge than the other one. So, since electricity moves from greater to lesser concentrations it's going to transfer that extra juice to the other battery. And once that gets it, then it will have more energy, so that energy will go back to the original battery. This continues indefinitely, they are basically shooting that small charge back and forth which after time (a few days usually).... kills them both. I've tried it once despite knowing this, and after the car sat 3 days I came back and both batteries were dead, and wrecked. For a winching setup, you're best to have an isolator to let those batteries be charged by the same alternator. Picture this: You're in the middle of nowhere and stuck. You have to winch yourself out but it was a tough spot and all of a sudden you don't start. You are SOL.... With that isolator you can keep them seperate, say you do kill the one battery from winching (a deep cycle of course), you simply wait a bit for it to charge.
I don't have a winch, but my situation is this: I have the tunes cranked and the battery goes dead after an hour. I just walk up, flip a switch in the cab and start the vehicle up with the other battery. Check out Hellroaring for an isolator. Sorry for the long post, I don't claim to be an expert but I know what I'm talkin about. Good luck!

 

Jus wondering about this whole suggestion of two batteries I ain't a real rock crawler I used to jus build small yotas for speed and crap n help around with my uncle with the big ones for mudding...aaaaanyways I jus moved to Cali n bought a 94 4runner and don't kno what the hell went rong but i tested my alt n its good and I put in a brand new battery but my voltage meter drops wenever I turn on a blinker or roll down a window! Anybody can help me please I'm a not a real electrical man n I checked grounds and all but all I can see is my alt cable being a little blue but I don't kno if it's the prob? It aint even corroded...I wanted to put in another battery but not sure how to wire it...jus for som sounds so my lights dim on me...and thinkin bout the gm alt swap..anyone suggestions or advice