2nd battery + isolator, more strain on alt ?

10+ year member

I was thinking of adding a 2nd batter with an isolator , ofcorse, but then i was was thinking, ;; wouldn't a 2nd battery put more strain on my alt ?! ;; because my 2nd batter would power my "" eq/radio/2 highpower amps/dvd player/neons/ "" but this batter would be drained and the alt would have to charge it,along with charging the primary battery.. is this ture is this how it works ???


10+ year member

Hebrew Israelite
Good question.

I'd like to know that answer too. I currently have an isolator and a 2nd 800amp battery.

I don't know much about the whole picture, but I see like this..."Maybe" your alt might be working a little harder to charge a 2nd battery, but if you didn't get one and your alt couldn't keep up with the current demand, AND you drained your one and only battery, you'd be in some sh*t,lol. You might end up asking someone for a jump.

I think reserve power is a good thing. And if you aren't going to get a more powerful alt, then a 2nd battery "might" be the best option for you.

I am very sure there are others on this forum that can answer your question WAY better than I can. Just check back in awhile, somebody will set you str8.



lexus rx
10+ year member

love tha bass
if your alt. is stock then it might work it but it would be nothing compared to not having the 2nd battery. doing what your doing is the best way to keep stress off all your electrical parts. the more backup power "batteries" the better. as long as you dont go overboard(10 batteries for 1 10" sub and a 300 watt amp!). the battery acts as a buffer for your alt. just think about it. say your pushing 1500 watts on an (xxx) amp alt. if you only have 1 battery your alt. is running at (xxx) amps just to keep up with the power consumption. if you have another battery there is reserve power there to help out with the power consumption. your alt. is going to have to recharge the battery but it wont be stressing the alt. as hard.


5,000+ posts

Kilroy was Here
If you only surpass the capability of the alternator momentarily and on occasion, then a second battery isn't even needed. If you run your system a lot with the engine off, then you might want to consider a second battery with an isolator for just the stereo. If you are constantly drawing more current than the alt can produce, then a second battery will make the situation worse. The deeper you discharge the batteries the more of a load they become on the alternator and the farther in the hole you get. A very vicious cycle. If you have any doubts as to whether your alt is up to the task, adding another battery will not help. Neither will a cap. Only a bigger alt will help.


10+ year member

well i belive my alt is 70 amp, i dunno it could be higher sence a 100 amp fuse is between the batt and alt .?.

no as for my alt being up to the task or not, i dunno yet as i have not yet installed my hc 12" and my other set of cdt cl61's wit 2 black maxx amps, but i have had a dual amp setup b4 in my car, a performace tek 1000 watt and a dhd power cruser 1600 watt, and when the car was running and the bass was thupin volts would drop from 14 to 13, and idle would get weird,

(drop lower when bass would hit)

i mean even though i had a 1.2 fared cap it didn't really didn't make a big difference, i dunno i guss i'll know when i install all my sh*t and run it...

thanx fer thhe replies

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