P/N: 103-304742, 2XER18505M. Visonic PowerMax Siren Battery & Window Stickers. Compatible with the following Visonic sirens: MCS-740, SR-740 PG2. Type: EVE Lithium AA Battery, ER18505M. The originally issued battery should be replaced every 2 years to ensure your alarm has enough battery power to sound the alarm in the event of a power cut.
eBay