Sure can, but unless you have a 20 ohm atty or don't mind horrific converter efficiency why would you need 14.8v?
More details of the mod are required in order to advise if the mod is feasible or reasonably functional for the intended goal. But the only answer to your question is that, yes, you can stack batteries in any number of your choosing as long as its done with a little proper prior planning. Ie: matched resistance, quality cells, ect...