Shunhong 6-GFM-38 replacement 12 volt sealed lead acid Battery: Amazon.co.uk: Electronics & Photo
Mighty Max Battery 12V 12AH Replacement Battery for 6-DGM-12, 6-FM-12 Rechargeable Sealed Lead Acid 12120 Backup Power Batteries in the Device Replacement Batteries department at Lowes.com
Amazon.com: SPS Brand 12V 18Ah Replacement Battery for Enduring 6FM18, 6-FM-18 12V 18Ah UPS Battery : Health & Household