My team wanted to reduce the amount of extra electrical components on the robot, so we used the Vex batteries which are also 7.2 Nickel Cad, which are allowed under rule R68 (IIRC), which allows any replacement backup battery. You get longer runs with them, and charging them is the same as charging RC batteries, so they can be quick charged in 15 minutes, so with two there should be almost no downtime.
They do add a bit more weight, but it is negligible compared to what you get in return, which is extra power for the camera and servo's as well as anything else that gets it's power from the RC through the backup battery.
Edit: Seems I had already told my story, sorry for the double posting
