10 Year Lithium Battery. Compatible with SW1-PF-T, HW1-PF-T, CW1-PF-T for wireless interlink. This range of mains with 9V battery back-up features unique Push2Fit bases for quick and easy installation to save you time and money on installations. The unique Push2Fit base included with every mains alarm has been designed to ensure a secure and speedy connection of the alarm to the base unit, saving you time and money on installations.