Just upgraded my stock system w/new speakers all around and a kicker component sub with a 300w amp.

Worked fine the first week, then the car started shutting while idle. Starting up was a problem as well. All the lights on the dash flickered and my car didnt start. Took it in to autozone and they checked, apparently the previous owner had put the wrong battery. Its a L4 2.4L Vtec and he put a bigger battery made for the V6.

What would you guys recommend doing? Changing my alternator to a higher amp output? Or just replacing the battery with the right fit. If so, then which battery do you recommend? Considering my small low watt system.

A bad battery could cause that, it wouldn't matter if it is oversize or not. There is no reason to change the alternator unless it is malfunctioning. If it was mine I would have the battery charged and load tested. That will tell you positively if it is good or bad.

put in the "wrong battery" i'd like to hear the explaination of that:paranoid:

The V6 battery is considered an upgrade. I did it earlier this year when my stocker began to fail. I purchased the larger battery tray and heavier gauge ground cable from my dealer.

I'm with RTF, have the battery charged and load tested. Have the alternator checked as well. I'm not sure if a higher output alternator is available or not. Good luck with it.