Dual batteries - United Bimmer Community

**Dudesky** · 06-30-2006, 06:01 AM

Anyone have experience with dual battery setups?

My bro-in-law has a conversion van that uses 2 batteries, but the auxilliary battery is missing. I assume the isolator is supposed to keep the two seperate, but I can meter 12v on the auxilliary side where the cables are supposed to connect to the 2nd battery. Which means that voltage can only be coming from the primary battery . . is this normal? I don't wanna hook up the 2nd battery and end up blowing them up

Sorry for the non-BMW post

**c1apton** · 06-30-2006, 07:23 AM

Depending on the ISO yea that's normal. TIP: for aux battery - get yourself a marine deep cycle battery. They're tougher and can take massive amounts of abuse.

**Dudesky** · 06-30-2006, 08:01 AM

Thanks, I wasn't sure . . I'll have to check the cables for the 2nd battery. I'll install an inline circuit breaker or fuse (if there is none)before connecting everything, just to be on the safe side.

**notop4me** · 06-30-2006, 08:08 AM

Yeah, deep cycle is used by most for secondary. These setups are recommended usually for massive stereo systems where a few farads of cap just isn't enough. I've always thought it was in vehicles used in sound competitions only.

Ken

**xsperf** · 06-30-2006, 09:43 AM

are the two batteries parralell or in a series, or are they totally seperate? btw, a lot of times the meter that reads your voltage, its actually the voltage of the charging system, so if your alternator is working and you have a dead battery, it will read 12 volts....

**da_bull** · 06-30-2006, 06:00 PM

the deep cycle batteries actually dont give up current as fast as a regular batteries. they are designed more for applications where you need a small draw for a long period of time. they also can be drained until dead and are able to be charged back up with less damage to it than a regular battery.

the isolaters are nice because you can totally drain your battery (parking lot, key off time) and start your car to go home.

**Rooz** · 06-30-2006, 10:11 PM

For Audio systems... I would not recommend it because for one, your alternator isn't made to do this at all....

IF you are doing this for audio, you might want to consider an SVR deep cycle audio battery

**Dudesky** · 06-30-2006, 11:12 PM

This isn't for my car; it's for my bro-in-law's conversion van, which has AC electrical outlets and a breaker box inside, for RV purposes. It was just missing the aux battery, and I wanted to make sure one battery wouldn't simply drain into the other . . guess I'll find out tomorrow