BX1500G vs SU1000RM2U -- Fewer batts, yet more power?

[Anonymous user]

Up until a few months ago, I was using a pair of SU700's, which each use 2x 12v7Ah batteries. I then started using a SU1000RM2U which uses 4x 12v7Ah batteries. I started wondering if I should just get another SU700, so at least I'd be getting 1400VA out of the four new batteries I just bought.

Now I see a good deal on the Back-UPS BX1500G. I understand it's for the Home/SOHO market... but it looks to me that these use 2x 12v7.5Ah batteries (please correct me if I'm wrong about the batteries!). What gives? How are these about to use (about) half as much battery capacity, yet are getting 50% more power than the SU1000RM2U? Is it just that these new units using a FAR more efficient inverter? Should I ditch my old SmartUPS units and buy a BX1500G instead? Besides the smart slot, is there any reason to keep using the SU1000RM2U?

Thanks for any insight you folks can provide!