This replacement battery is 100% compatible with the Ascom d63 phones and battery chargers. The 1200 mAh capacity rating is guaranteed to extend phone Talk Time by 30% or 4-6 hours longer than the Ascom 660497 (black), 660507 (white), and 490933A (both) batteries, which only offer a 920 mAh capacity rating. Battery uses Japanese power cells from Panasonic which are proven to deliver maximum battery run time and total cycle life.