Battery Life

[cilginbilgin]

Hi,
We are having a big issue with the life of battery on the robot. Even we charge the battery until it gets fulled, it only lets us 20 minutes of practice. Moreover, depending on the change of voltage on battery, the robot doesnt do what we say in the code especially in autonomous. What else can be done to solve this problem ?
And one more question: Are we going to be given charged batteries before every match at the competition ?

Thanks guys!