I have four 90 watt Polk Audio speakers connected to an amp that has 360 continuous power or 720 max. I had it wired to a deep cycle battery and it played fine all summer. Now it will only sound good with the engine running. With the engine off the speakers sound distorted. I checked the voltage at the battery with it running and with it off and it measured 12.8 volts each way. I tried running another battery in parallel and had the same problem but with that it was also distorted with the engine running. My guess is that the alternator couldn't keep up. At this point I am stumped. Any suggestions on how I should proceed?
