Mike,
About batteries. They make very nice ballast (if any ballast is required)! No one ever has 'all' the battery that they wish they had, and substituting another battery or two for any ballast you might need is an alternative.
Also, if you have the option, using geared motor(s) instead of directly driven props, ~usually~ means less battery drain and longer running times. You have to balance that against the higher cost and complexity of geared motor systems, though, and there are other 'draw-backs' to geared motor systems (noise mainly). That's not a suggestion, just an alternative.
- Doc