Increase UPS run-time with bigger batteries?

[longneck]

i have two UPS's that protect my computers and entertainment system. I'm at less than half the kva rating of each of the UPS's but the runtime is too low for my liking. they both run with 4 qty 6V sealed lead acid batteries.

my question is: can i simply use higher AH capacity batteries provided they're sealed lead acid, and the total voltage is 24 volts?

 

[Metallicbeing]

You could increase the run time of the UPS by increasing the amp-hours of the batteries. However, your UPS is only rated for the batteries they already have. It would be best to buy a larger UPS that is rated to handle the larger batteries.
Another thing that would affect runtime is battery condition. Batteries in your UPS should be changed every 2-3 years. If you notice that your UPS is running at a low output voltage (< 100V) early in its tranfer to backup power, then you should change your batteries.