The EY9L10B is a 3.6 V lithium-ion 1.5 Ah battery pack that is 40 per cent lighter than Ni-Mh and Ni-Cd batteries, and has an expected battery life of eight years. The driver includes a battery protection feature designed to prevent excessive discharging of the battery pack. The battery protection feature activates immediately before the battery loses its charge, causing the 'battery low' warning lamp to flash.