cr0sh:
What do you need the 12 volts for - the router? Whatever, it would probably be easier and better to get a couple of 7.2 volt packs, wired in series (make a "y-cable" that allows for this, so you can disconnect each to charge the batteries), then drop the voltage down with a 7812 regulator (and if you need the current, use a bypass transistor - or even better, see about getting a drop-in 3-pin switching regulator for 12 volts). Ultimately, you're likely to get a better system with a longer runtime going that route. So far, though, your machine is looking great!
Yep, I need 12V for the router. I'm considering your solution, but the up-voltage IC would be easier to add to the controller at this point. 