Doing some research for a project, I came accross Saphion
U-Charge batteries (from Valence). In 15 lb, they pack 45 Ampere - hours at 12 volts, and have a lifetime of 2000 charges.
A lighter battery is the Ultralife UBI-2590
UBI-2590 . It weights about 3 lb and has a capacity of 12 Ah at 14.4 volts OR 6 Ah at 28.8 volts. FOUR of them would fit within the battery weight of the robot, and would provide 24 Ah at 28.8 volts. That voltage can produce over two
horsepower from a drill motor. I don't know about CIM's but it says "12 V DC", so it might not be a good idea to try it. Batteries have a future, just not lead acid ones.