question on stick pack voltage drop

[MIcrawler]

i am running 8.4v 3000mah stick packs in my rig... i got about 20-25 minutes of run time with 55t in R2 trans with 12t pinion.... when it started getting weak i swapped out the pack with the other one.. they were both at 9.55 volts when taken off charger... and when they were hardly running the truck they were down to 7.5v does that sound about right?? I guess I always thought it ran down much lower then that...