Nobody else has mentioned it, but first you could try a different prop. I
picked up a prop called a Kipawa and I love it. A friend of mine suggested
it. Supposedly you get more power and speed and more efficiency at the same
time. I do have a 24 volt system but I definitely noticed more speed and my
batteries seem to be lasting fine. I think it ran me about $40, might be
worth a try.

Rich P

Here's the link:

http://www.kipawapropellers.com/