SLA Battery Help

I have a Merida PC500 I bought. What are the differences in all the different brands of SLA Batterys? I need 2 12 V 9ah batterys for my bike. Has anyone used the Tempest brand batteries from BatterySpec.com? They seem to have been in business for quite awhile. The prices and shipping charges are the best I found the web.
What is the difference between a UPS replacement battery and a Scooter battery.
Thanks for any help