Matt, if you push the LiPo against the back of the servo the hump DOES rub on the pulley. That is why I centred the bump between the pulleys, marked up the position, and glued the battery locators to the bottom, and then doubled it up by using the velcor to make sure it won't move. It works fine.
In retrospect, it would have been a lot easier to get Trakpower LiPos and then the position wouldn't matter. But I didn't know that when I bought the kit and battery
Rossi, I'm not sure if I can really be bothered doing that. Sounds like a lot of work. If it splits I'll just buy a new bit, I think.