With 10KS UPS backup for an hour. How much AH battery is used. How many only. Speed back down. Load is 8KW .. DC is 240
You did not tell people how much load, how to calculate ah!
Battery capacity ah = load capacity / 0.7 (discharge factor) / efficiency (depending on the efficiency of the UPS you buy) / battery voltage * emergency time (hours) because you did not tell me the specific load and your UPS efficiency, only Your own calculations.
Let you give the information, the theoretical value of 20 38AH battery enough, but to consider the lack of enough battery problems, if you want to buy garbage batteries, you have to have 65AH battery, but also 20. Good battery estimation such as Panasonic battery, you can consider using 38AH battery.
But I would like to remind you that the load is 8KW ups peak, the general ups is recommended to load 80%, so ups life will be long point. And you have to figure out the power factor of your 10KS machine, if it is 0.7, then you can not afford the machine.