What battery would you recommend for powering 10 servos at 6v?

I am currently working on a humanoid robot and am trying to ruduce the weight and increase the opperateing time I am useing 4 AA batterys to power the top half 12  servos and another 4AA batterys to power the bottom half 10 servos  22 servos in total . The AA batterys tend to go flat quite quickly and haveing 8 AA batterys make the robot heavyer also if i could recharge the battery it would be a great help. the servos are rated at 6v maximum and 4.5v minium what would you recommend ?

Any help is greatly appreciated.  

You could move to LiPo

You could move to LiPo batteries, which have very high power to weight ratios.