Amazon.com: Replacement for APC Back-UPS 600 BN600 Battery - Replacement UB1290 Universal Sealed Lead Acid Battery (12V, 9Ah, 9000mAh, F1 Terminal, AGM, SLA) - Includes Two F1 to F2 Terminal Adapters :
APC RBC32 (12V 9AH Version) UPS Battery Set (Replacement)