Panasonic KX-TCA200 Battery Back-Up Power Supply Battery size: AA (4 for 6 V phones, 6 for 9V phones) Talk time: Up to 3 hours Standby time: Up to 5 hours Compatible with Panasonic 2.4 GHz and 5.8 GHz cordless phones, excluding models prior to 2004, KX-TG2000, KX-TG4000 and models after 2006