So I'm buying my girlfriend a sub and amp for her car. I figure with the combo her lights will be dimming on the stock wiring she has I don't have money to buy a new battery and big 3 for her car right now so which would be a better option? I know I can buy the stuff for big 3 for about $45-$50 and a new battery would be probably $150 but would a new battery give the amp more juice than the big with with stock battery? I plan on getting both down the road. Which would be best to upgrade first?