I have a car stereo, two speakers, and we are wanting to add two wireless outdoor rock speakers. I am looking at this, Pyramid PS14KX 12 Amp Regulated DC Power Supply, will this be enough? I dont need a ton of volume, just some tunes around the pool. Why is a battery needed as well? I dont know if I want to go through the trouble of setting up a battery and a charger to go under the outdoor kitchen. Will the stereo burn up the power supply eventually?