Interesting that yours came off at a lower voltage.
Not realy, well maybe its interesting, but its also predictable.
Kinda hard for to explain in a forum, but this is still voltage sag (probably worth googling instead of reading my golboldy gook that follows)
(google it now)
(its still not to late)
lets say you have a shiny new 100 volts battery, its just sitting there, you put a volt meter on it and its exactly 100 volts (because is hypothetical!). Now we directly connect your standard 10t 20amp (sure why not since were making up numbers anyways) hypothetical dc motor on the battery, you might believe that we are giving that motor 100 volts. Well were not, were actually giving the motor 75 volts (more made up numbers) because the amp load on the battery is more then the battery can dish out. After a minute of running the motor we disconnect it, since we already have a volt meter watching the battery we will see the voltage rise form 75 volts to 99 volts.
Now if you have a low voltage alarm set to go off at 76 volts it will trip as soon as you connect the motor, even though your battery reads 99 volts when you have removed the motor. That is voltage sag.
This time we just got 50 shiny new 100 volts batteries and we wired them all in parallel, we put a volt meter on them and we get 100 volts (hypothetically predictable). Now when we put our 10t 20amp hypothetical dc motor on the battery our voltage drops to only 95 volts instead of 75 volts. The voltage sag is much less because combining the batteries in parallel lets them pump out more amps at once, and your dividing that 20 amp draw over 50 batteries. So each battery acts like it has a 0.4 amp load.
So running batteries in parallel will help to limit the effects of voltage sag.
on an rc car the esc and terrain make the amp draw constantly change. Increasing the amp draw increases the voltage sag.
The maximum amp draw you can put on your battery is by completely binding up the motor and giving the car full throttle. (you probably don't do this)
One of the next biggest amp draws mashing the throttle from a dead stop. This can be like 10 times the amp draw of normal driving, and its high amp draw will cause extra voltage sag that will trip the low voltage alarm prematurely.
(I bet you wish you just googled it like I told you in the beginning)
So thats part of why my casual driving driving on a new battery had a lower voltage when we measured them then your more (I cant remember what word you used) extreme driving on old batteries. When the low voltage alarm tripped, both batteries were actually at the same voltage of 3.2