i went to the LHS today and picked up a speedpack 8.4V 7-CELL HUMP Ni-MH 5100 mAH battery for my Traxxas Stampede XL-5 they said it should be at least double the stock battery time and im sure they said it should last at least 30 minutes but i timed it and it lasted only like 16 minutes 20 seconds is that bad? does it get better? please help me
Ty

