Choosing the type of battery for a project
You can derive some ballpark values from the performance specs of the servo. At full torque (4.8 kg-cm) and speed (0.1s/60&deg;), it's producing about 5W of mechanical work. Taking various inefficiencies into account, each servo can reasonably be expected to draw over 1A of peak current.

It really depends on how much work you're expecting the servos to do over those 8 minutes (collectively, on average). Worst case, you could be looking at 10A full time, which would require a battery capacity of 1.33 A-h per run.