Tell us about yourself!
I made something very similar but I charge the batteries using a 80W solar panel and I use a TDA7492P amplifier intead of a car radio. I already burned a couple of hifi speaker's coils due to the 'high power' of this amplifier. So, I'm thinking of using cheap car speakers. Because I can use car speakers with a hifi amplifier, right? I'm asumming both speakers work in a similar way.
HacKeyboard, a mechanical keyboard built from scratch
Homemade GameCube Mod-Chip
5V breadboard mini PSU