As long as they're AGM and have adequate capacity I suppose it does not matter. Cheap flooded batteries are a poor choice for UPS/SBPS though. Flooded systems are used by telcos but they are designed for this purpose from the ground up including proper venting of explosive gases, intrinsically safe fixtures, etc.
Small SLA is fine for sufficient run time for the facility transfer switch to engage and the genny to come on line and synchronize, etc. Flywheel systems are also good for this type of operation. Of course I cannot imagine anyone (outside of a character of fiction - Tony Stark) having such a system in their house! :laugh: