If the charge time is 50 minutes and the charge current is 4.5A, then you do (50/60) x 4.5 = 3.75Ah input.
Is that what you wanted?
The most common question on this sort of thing is the numbers on the matched cells, for example 512 seconds at 30A
In such an example, if you wanted to know the discharge capacity then you divide the runtime in seconds by 3600 (the number of seconds in an hour) and multilpy the answer by the discharge rate (so 512/3600*30=4.26Ah).
ps - if anyones actually belives you can get 512 seconds from a 4200mAh cell at 30A then you are deluded...
