I have searched for DAYS without finding any real answers so any help is much appreciated.

What is mAh? Is this the amount of power that is stored in the battery pack or in each cell? So the higher the mAh the longer the run time?

7.4v and 11.1v, this is what the Battery outputs to the motor right? So the higher the voltage the faster the engine will go but shortens the run time?

If I have a 2cell ,3cell ,6cell, or 8cell battery pack all 7.4v and the same mAh. Is there a difference?

The reason for these questions:
Ok so I have a fully modded MIST and a stock one. I want to buy the Thunder Power eXtreme 2200mAh 7.4v (for the stock one) & an 11.1v (for the modified one) will that be fine?

Modified MIST:
MIST KMRC conversion
6000 Hyperion CC mini pro ESC
6800 Mamba motor (backup)
Everything else can handle the power and torque

Stock MIST:
Stock!!!!