2000 Saturn SL1 Battery

Electrical problem
2000 Saturn SL1 Front Wheel Drive Automatic 130000 miles

Ok so just a few days ago I had recently installed an amp and 2 subs in my car. Everything was working fine until just this night. After being turned off outside in the cold four a few hours I went to start it up but it like sputttered and had a hard time starting. So I turned my amp off and it started but I had to keep pressing the gas while turning the key.(Ive had to do this ever since the 1st time my battery died after leaving my lights on) but I could always get it to start and it was fine. But now it seems like the lights get dim everytim I let off the gas and I have to keep reving it to keep it running or it will die. Im thinking my battery is low or needs to be charged. It is a 2000 and I think its the same battery thats been on it never changed. So what do u think. Should I get a new battery or what? Im sure its because og the time I left my lights on and it died. I jumped it and it worked fine except for the needing to press the gas when I turn the ignition. Also it was working fine earlier in the day before school then after school. But at night when it was colder is when it happened.