last week I went wheeling with a friend and I got stuck pretty bad. I started using my winch and notice that the winch consumes more power than what the alt can charge. I already knew this so I decide to get an aux battery. I already have the battery but I dont know how to connect them. I know that if I connect the +'ves and -'ves both battery will drain at the same time. I want just the aux to drain when winching living the other to run the car. I have research and it looks like a good option are some voltage sensitive relay that automatically switch between batteries. however, I don't know if this relays work even when the motor is running.

has any body done this in his truck ? what are your advices? thanks

Most RV and boating supply stores sell a "battery isolator relay" for 20-35 bucks. The two contacts this relay can be connected between the positive terminals of your starting and auxiliary batteries. The relay coil can be connected to the "run" position on your ignition switch, so that the coil is only energized when the engine is running. Finally, the negative post of your auxiliary battery is connected to chassis ground, same as your starting battery.

RESULT: Both batteries are connected in parallel whenever the engine is running (thereby allowing the alternator to charge them both), but isolated when the ignition switch is turned off.

This is the same scheme that most motor homes and many boats use - It's simple, and effective.

My brother has a duel battery with one as a designated starter and the other for all of his aux. electrical. He went with an isolator to do the job of charging when needed. Check out the "painless" site:

http://www.painlessperformance.com/...partsearch=isolator&submit=Go%21

A simple phone call to one of their reps. will give you tons of info. about suggested components for your situation.

To monitor the battery charge he installed a vdo gauge with a toggle that can switch between each battery.

Hope it helps.

I would check that out. thanks for the info

I am gonna look for that relay online and see what's out there thanks.

Solve the problem instead of putting a band-aid on it. Upgrade your alternator to something that can handle the draw of the winch, coupled with a good AGM battery and you won't have to worry about dual batteries.

totally recommend the dual battery setup with AGM batteries.

this way, you can use a fridge all night along with lights and other accessories and start your truck in the morning after camping.

all you really need is a high amp relay to handle the current that your alt puts out.

you put this between the batteries on the + cable and trigger it with an ignition wire from your key.

when key is off, batteries are isolated

when key is on, batteries connected so you have maximum starting power and then both recharge as you run the truck.

my brother went camping with us and had his fridge on over night; couldn't start his truck in the morning

If you plan to use a fridge or other accessories far in the outback areas, it is always a good idea to have two batteries running your system, especially if you go alone