What does C mean in a battery?What does 1C mean? How to measure capacity 1.5Ah ?

1.5A means the battery can be used for 1 hour according to 1.5A continuous discharge, so it can be used for 2 hours with 0.75A discharge. C represents the discharge rate, the battery is 1.5Ah, 1C, then the max. charge and discharge current of the battery is 1.5A charge and discharge multiplied by both.