[MrForbes]

You might try scheduling more practice sessions, and have them be of shorter duration. I don't know how many hours a day you practice, but it must be more than an hour at a time if you're not able to get it done with 10 batteries that each last 6 minutes.

If you have to spend more than an hour practicing, then you might try using the batteries when they're only about 75% charged, and limit them to 4 minutes of operation.

Or schedule a five minute cooling off period after each five minutes of driving.