Exactly what I was going to suggest.

If you want more capacity and lighter weight in order to attach it to the starter (if this is convenient), you can use a 4s lipo with high C rating. Most starter motors have ample tolerance for increased voltage like that.

BTW Crank, I use a 3s lipo in my TX for power and the radio just sings along at 12V all day long. I think it could take 2-3 days of flying before the pack needs recharging but I'm not going to try that... [X(]

David.