Amazon.com: Power Sonic 6V 4.5AH SLA Replacement Battery for Jasco RB640-4 Pack : Health & Household
Jasco RB640 6V 4.5Ah Replacement Battery (6 Pack)
Mighty Max Battery 6V 4.5AH SLA Replacement Battery for Jasco RB640 Rechargeable Sealed Lead Acid 645 Backup Power Batteries in the Device Replacement Batteries department at Lowes.com