Do you have to use the same battery under the hood?

[jkok7 10+ year member]

First, it doesn't matter where the guy you bought it from set the gains. The gains are set to your head unit, NOT your subs.
Second, once your car is running, it is running off of the alternator...NOT the battery. The battery only starts the car, then the alternator drives everything. If the car dies at idle, and will not start back up, I'd start with checking the alternator. I know Autozone will check it for free.

I only broutht that up because to eliminate any concerns of thinking somethins wrong with the amp. The gain can go past where I set it. That's all.

 

[Chrispy 10+ year member]

Use a DMM to set the gain.