thinking about running a second battery in the trunk. i was told there are two ways of doing this. 1, using a isolator and 2, running the + from the front battery all the way to the second battery and then ground out the negitive. are these both true? what should i do?

Both are true.

The difference between the two depends on how you like to listen to your music.

If you like to listen to the music with your car off for long periods of time, get an isolator (so you don't drain the starting battery). If you don't need that functionality, than just connect the positives together. Ground the negative to the chassis. You also should put an inline fuse within 12" of each battery to prevent shorts lighting your car on fire..

Pretty much the point of the isolator is to prevent your system from draining the front (starting) battery if you're playing with the car off. Chances are you don't need one, and could do exactly as you mentioned:

Run a + line (fused of course) from the front to the + of the battery. Easiest with the - is to just find a good point to ground it to the chasis.

thanks for the fast response fellas. shops like to try selling you things you just dont need. I can aways count on my Fi crew. this is for all the shops that dont know what the BIG 3 is......

another thing, will running a second battery without the isolator overload my stock alt? 2001 saturn L300

No one stock battery and an extra in the trunk won't "tax" the stock alternator...

The isolator has nothing to do with the alternator, in fact in simplest terms the isolator is off when the engine is running and on when the engine is off...

Some argument can be made that the only "effect" the isolator will have in regards to the alternator is resistance between the alt and the batteries....

In short if you like to play the stereo with the car off get an isolator

with the engine on... no isolator

If you plan on running more then 2K watts upgrade the Alternator to a HO Alternator based on the amps amperage draw rated through it's efficiency...

Edited August 25, 200718 yr by theabunai

thanks again. i will run a second battery in the trunk with no isolator, using my stock alt and front battery. i'll let you know how it went after the install.

im trying to do the same thing, is it better just to buy a yellow top battery or to get another auto parts battery like my stock and put it in the trunk??? what would be the good of adding a second battery without an isolator?? do both batteries have to be the same size cause ive heard that if one is biger than the other both can drain each other is that true??

1. im trying to do the same thing, is it better just to buy a yellow top battery or to get another auto parts battery like my stock and put it in the trunk???

2 what would be the good of adding a second battery without an isolator??

3 do both batteries have to be the same size cause ive heard that if one is biger than the other both can drain each other is that true??

1 and 3- It can make a difference if the batteries specs are too far off. Generally it's a good idea to run the same type of batteries throughout just to prevent any issues.

2 The same good as adding a battery with an isolator, unless you like to park your car and play music for hours with the car off.

Pretty much the point of the isolator is to prevent your system from draining the front (starting) battery if you're playing with the car off. Chances are you don't need one, and could do exactly as you mentioned:

Run a + line (fused of course) from the front to the + of the battery. Easiest with the - is to just find a good point to ground it to the chasis.

^ posted at the same time, otherwise I would've just 2nd the motion

UPDATE: installed a second battery( stock, same as front 675 cca) today with no insolator. with one battery, i got a low 10.7 out of 14.4 volts. since i installed the second battery, the lowest i get is @ 12.7 - 13.5 volts when hitting bass. i can tell that my amp is staying strong the whole time. battery and parts...$150. installing time....3 hrs. 143db.... PRICELESS