Hi Chris, the problem is the battery MAh. The Standard battery supplied is a 7.2V 1800MAh-it isn't the voltage that is the issue but the MHa. Once that starts to drop the tank will have issues. You are correct, a standard battery will give you 10 to 15 mins run time. I use 7.2 V 3500MHa, this gives me a run time of 30mins or even more, the trick is not to run too much at full speed. The batteries I use last me all day at our home events, run for 5-10 mins, stop then start again, just turn off the tanks when you have finished. Now, the 7.2V get slightly bigger in size the more MHa there is, yes, run time is extended but, they will not fit into the tank, to remedy this you have to perform surgery and replace the hull screws with magnets, cut out the internal battery box frame, make a false bottom. You can of course go the LIPO route, but you need a special charger, charging bag/storage and you may have to change the whole MFU board from a standard Nicd one to a different one like a IBU board that is costly.
