I am building an Xbox 360 Laptop, and obviously it can't always be plugged in :P. Where would I be able to find a rechargeable battery to kick out at least 175W, 12V, and 42A (DC current)? Ideas and suggestions are also welcome!
You will not find one tp fit any machine. this is far too high a load . In act the only batteries capable of this kind of output would be lead acid, as in small car batteries. I don't think they will fit in the case. And can not be safely carried due to acid spillage risks.
