on my rear battery i have running..
sub amp
tweeter amp
mobile phone
invertor -- pc psu
pc psu -- amd k6 450 b+p
isa 10" controller card
agp graphics card
sound / tv / nic cards
40x4 lcd
keyboard + trackerball
CD Rom drive
and soon 2x webcams
dag namit its not overkill, its just fun!

I wont/dont use the cdrom keyboard agp gfx card most of the time so i save battery usage :P

I think I get about 1 hours tops playing mp3s w/ amps on.. i'd be very lucky to get any more =[

thats on a diesel battery, I want a solid state but my bank account sais different..