Hey guys im trying to trich out my little bros little tike hummer help pleaz?

I took the seat out and put in a small sherwood 500watt amp and a pioneer DEH-P5800MP and i also put in two 4x6in kenwood Speakers its play and all but i dont get that much power after i take it of the power from the wall plug any help on wat i can do?Hey guys im trying to trich out my little bros little tike hummer help pleaz?put a second 12v battery in it to run the stereo system