Second Battery, dont you need an isolator?

[silenkiller 10+ year member]

If I'm not mistaken, don't you need some method of separating your cranking hood battery from your trunk battery to keep them from discharging each other? Not sure how to go about that, could anyone point me in the right direction? I'm getting a 200 amp alternator soon and I figure I mise well slap in a trunk battery too.

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[01 S 10 10+ year member]

its more of an option. I have a red top upfront and two Xstatic Batcap 800s inside, no isolator. I can play the system for hours and still crank it up in 1 second.

you should not need one, unless you found it would be useful in your particular situation.

plus, there are plenty of stock vehicles that come with 2 batteries already (large suburbans and F350s and sh*t). I dont think they would discharge each other.

 

[mokedaddy 5,000+ posts]

Unless you plan on playing your system for hours at a time at full tilt they really dont have much place in car audio.

 

[seedubs1 10+ year member]

I think what he's getting at is that in parallel, voltages are equivelant. So if you are using different batteries, shouldn't you have to do something about the voltage differences, or the batteries will try to reach some sort of medium resting voltages (draining one with the higher resting voltage in order to supply the lower resting voltage batt.)?

I think if the resting voltages are fairly close, you shouldn't have a problem. Problems here really only occur when you have an old battery that is going to die soon and keeps trying to discharge the good batteries to keep it's voltage up.

Did I get that right? My brain is kinda fried right now from studying for ME finals:crying:

Or maybe he's just getting at trying to have a battery that will still have enough juice to start his car after he's done draining the other batts.

 

[silenkiller 10+ year member]

So basically your just wiring your batteries in parallel then. Now, are you wiring from alternator to cranking battery, then cranking battery to trunk battery? Or two wires from your alternator to each battery?

 

[silenkiller 10+ year member]

I think what he's getting at is that in parallel, voltages are equivelant. So if you are using different batteries, shouldn't you have to do something about the voltage differences, or the batteries will try to reach some sort of medium resting voltages (draining one with the higher resting voltage in order to supply the lower resting voltage batt.)?
I think if the resting voltages are fairly close, you shouldn't have a problem. Problems here really only occur when you have an old battery that is going to die soon and keeps trying to discharge the good batteries to keep it's voltage up.

Did I get that right? My brain is kinda fried right now from studying for ME finals:crying:

Yes, there we go. Thats what I mean

 

[mokedaddy 5,000+ posts]

I think what he's getting at is that in parallel, voltages are equivelant. So if you are using different batteries, shouldn't you have to do something about the voltage differences, or the batteries will try to reach some sort of medium resting voltages (draining one with the higher resting voltage in order to supply the lower resting voltage batt.)?
I think if the resting voltages are fairly close, you shouldn't have a problem. Problems here really only occur when you have an old battery that is going to die soon and keeps trying to discharge the good batteries to keep it's voltage up.

Did I get that right? My brain is kinda fried right now from studying for ME finals:crying:

Yes that is correct, especially in theory. But there is also a .7 volt drop across an isolator so take that for what its worth.

But if your starting battery is crap an isolator isnt the answer. That would be a new battery up front. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[mokedaddy 5,000+ posts]

So basically your just wiring your batteries in parallel then. Now, are you wiring from alternator to cranking battery, then cranking battery to trunk battery? Or two wires from your alternator to each battery?

I know people that do it both ways. I just run it from the starting battery.

 

[ultimate157 5,000+ posts]

2 batteries won't drain eachother. If anything, the one with the higher charge will discharge into the other one, stabilizing the voltage potential to 0.