Brett,
 How many servos are you talking about?? You have to be carefull when going to a higher voltage pack. Higher voltage does not equal longer capacities. Usually higher voltage will give you more power in the servo as well as faster response times. But most times higher voltage will drain the battery faster. If you want more capacity you want to get a battery with a higher MaH (milliamp hour) rating. This will give you more run time with your system.

Ken</p>