My old backup system has lead acid batteries, rated at 105 A/h.

Why are batteries rated this way instead of W/h? Surely 105A * 12V gives 1260 W/h? 

And what does this mean? Can the battery deliver 12A/1260 W for an hour, and half of that for two hours?

Would it not be less confusing for lay persons such as myself to rate batteries by power rather than current? Would that not make comparisons easier?

7 minutes ago, Bobster said:

And what does this mean?

I found this Site useful and its still in my bookmarks, Ill take a piece from here to try and explain. 

"An amp hour (AH) is a rating usually found on deep cycle batteries. The standard rating is an amp rating taken for 20 hours. What this means for a 100 AH rated battery is this: Draw from the battery for 20 hours, and it will provide a total of 100 amp hours. That translates to about 5 amps an hour. (5 x 20 = 100). However, it's very important to know that the total time of discharge and load applied is not a linear relationship. As your load increases, your realized capacity decreases. This means if you discharged that same 100 AH battery by a 100 amp load, it will not give you one hour of runtime. On the contrary, the perceived capacity of the battery will be that of 64 amp hours."

Thanks. So it's not 105 amps PER HOUR. So if my old system is fully loaded, it will provide about 1.8 kw for an hour. It used to see us through a load shed without much trouble, backing up a TV, two standard lamps, decoder, wifi and one fridge. It certainly had it's uses. It once went 18 hours with that loading, but the batteries were never the same after that