Extra power


I was wondering if it was possible to have an extra battery in the trunk to power only the amps. When my subs hit the lights dim. So is it possible or should i just get a new alternator and capacitor? Thank you

Silver Member
Username: Carguy

Post Number: 236
Registered: Nov-04
Extra battery in the trunk won't help at all. Depending on your stock alternator size and amp, you might be able to get by with just a capacitor. Try this formula, 12V x 65A (for older cars and 75A for current cars) = 900W.
If your amp is below that power range minus heater/headlights/radio etc, then a cap might do the trick.

Silver Member
Username: Deathshadow

Post Number: 226
Registered: Oct-04
When the car is off yes but I find most new cars now (the ones I deal with) produce 14V + when they are running and warmed up.

Silver Member
Username: Deathshadow

Post Number: 227
Registered: Oct-04
Mine actually is on the high side; I read 14.5 - .7 volts with the car on @ idle and 13.1 with the car off (real good battery I guess).

Bronze Member
Username: Thrust

Post Number: 61
Registered: Nov-04
First I'd put a cap in there and see what happens with the lights. The setup you described creates more of a load on the alternator. Plus you'd need a multi-battery isolater. You really only need extra batteries if you listen to your stereo with the car off. Best option is to buy a high output alternator.

Okay thanks for the info. Now what kind of alternator and capacitor do u reccomend?
How about car audio batteries like optima?

Unregistered guest
You only need an isolator if you run your stereo
with the car off.
adding a second battery is better than a cap IMO.

Silver Member
Username: Carguy

Post Number: 249
Registered: Nov-04
Hey wangbar, 2nd battery is not always better than a capacitor. If lights are dimming slightly, a cap will fix it, where else 2nd battery probably won't help much. Glasswolf has an article on capacitor, it's worth reading.
The alternator I bought mine from was They should have one that fits your car. I found them cheaper than others. If you're going to get HO alternator get something around 170A or higher. That way you're covered for the future too. You can buy 1F capacitor from most manufacturers. They produce them using similar technology so you should be fine. Just get fooled into buying 50F or larger, you don't need it that big. Remember it's 1F per 1000W of peak power.

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5837
Registered: Dec-03

there ya go

Great articles glasswolf they really cleared up a lot for me
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