Some back-of-envelope doodling to make sure the numbers add up:
9.6V NiMH #1: 19.2 Wh / 5.0 cu. in. = 3.8 Wh / cu. in.
9.6V NiMH #2: 19.2 Wh / 4.8 cu. in. = 4.0 Wh / cu. in.
11.1V LiPo: 24.4 Wh / 5.4 cu. in. = 4.5 Wh / cu. in.
12V NiMH: 24 Wh / 7.2 cu. in. = 3.3 Wh / cu. in.
Example: 19.2 Wh and 2.5 Hrs of run time, average power consumption only 7.7 Watts. So must be a lot of stopping.
A web search found this 14.8V with a slightly lower mA-Hr rating but similar energy (25.9 Wh) as your other packs of similar size (6.5 cu. in.). As long as the Wh rating is the same between batteries the run-time should be the same for the same average power consumption. It's just that with a 14.8V pack you'll be able to reach higher speeds. I have no idea if this would fit your application but suggests a solution might be out there.
