Batteries do not generate energy. They store it and release it when needed. They don't store very much. Your amp can kill a single one in a couple of seconds. So adding a second batt simply gives you another couple of seconds. Your alternator is the only thing that generates electrical energy. So when you're talking about sustained playing, your alternator is what needs to keep up. No amount of batteries will allow you to draw more current than your alt can produce for an indefinite time period. Fortunately, we're not talking about an indefinite time period. We're talking about a song or two... and your system might keep up with that. That is what your voltage gauge is there for. You must constantly watch it to make sure you don't fall below 12.6v. If you're unwilling to do that, you don't deserve a stereo in the first place.I meant should I add another d3100 or what?
Alright so clamped power you are going to see much less than that. Assuming your vehicle uses ~50A for the factory electrical that leaves you with 220A of alternator to work with. On 14.4v, that is around 3100w of power that alternator can supply without potentially dropping, and since music is never going to make your amps pull 5k, you should be all set. But I agree with eCrack, a volt meter is always a good idea. A $10 volt meter can save hundreds and thousands of dollars of equipment just by being able to see where your system stands5k daily...