SO id like to make a portable PC for various functions using Raspberry pi, etc etc -

But the thing i am struggling with is, How would i power it. Is there any possible way i can make a self charging ecosystem by using some micro/mini alternator to recharge the battery as the system is running?
why wouldn't this work, using power to generate more power or so?

What would be the best next and viable option to powering this unit?

i know nothing about electricity or electrical systems when it comes to THIS kind of things...
which is why it confuses me why Electric cars dont have a way to charge themselves in an efficient enough way while operating to just keep itself charged... but thats a brain hurtin thing to discuss later, not here on this question XD