Considerations for long UPS battery life
CSB is a (Hitachi) brand name for the generic battery type called Valve Regulated Lead-Acid, or VRLA battery. VRLA batteries also go by the name of Sealed Lead-Acid (SLA.)
I don't know if CSB (Hitachi) VRLAs are any better than a competitor's (and there are many.) You should contact APC directly and get their feedback on using batteries other than the CSB brand.