Based on this product's specifications, here are some alternatives and similar models
Sealed Lead Acid UPS battery CSB GP645 — 6 V, 4500 mAh, VRLA, 48×70×108 mm, 840 g
Summary description:
CSB GP645 is a sealed lead acid (VRLA) battery designed for UPS and backup power applications. It provides 6 V nominal voltage and 4500 mAh capacity, with compact dimensions 48 × 70 × 108 mm and weight 840 g. ISO 9001 and ISO 14001 certified, suitable for emergency power, telecom, security systems and small-scale energy storage.