90a is equal to 5.4 kilowatt hours.
90Ah represents the capacity of the battery. When the discharge time is 1 hour (h), the discharge current is 90A, when the discharge time is 2 hours, the discharge current is 45A, and so on, when the discharge time is 10 hours, the discharge current is 9A.
As for the calculation of stored energy, the physical quantity of voltage is still missing. For example, if the output voltage of the battery is 60 V, the stored energy:
w=90Ax60v×10^-3X1h
=5.4Kwh。 That is 5.4 kilowatt hours.
