Quote Originally Posted by lerameur View Post
well it dissipates 1.54watt because it can take 1watt , so 2.54 watt total from the battery. I guess I need this part: L78S05CV for now
You could 'preregulate' the 12v input with either another regulator ( 12v -> 7809 -> 7805), maybe a few diodes in series, etc.etc. Knock the voltage down a bit before doing the final regulation to 5v. That'll cut down on your heat.

What package is this 7805 that you have right now? TO-92? TO-220?