Did the battery charge indicator light illuminate before the car died? If so the alt is done.. You will need a new battery no doubt. I would get the battery and try and start it (turn all your gizmos off obviously) and see if the indicator light is illuminated. If not then you may be good..just test with the multimeter periodically to see how it holds charge.. Also this will keep happening unless you get more power. Take it to a sound shop and get their advice on what you shuold do. You have way too much stuff for just the one car battery..