Replacement 800mAh 63421-01 Extended Battery for Plantronics CT11 & CT12 Cordless Headset Phones Replacement for: 63421-01, PA-63421-01 & PA-PL004 Batteries. Compatible with the following models: Plantronics CT11 & CT12 Cordless Headset Phones. 3.7V 800mAh 2.96Wh Ni-MH Battery. 1 Year Replacement Warranty MPF TM and MPF Products TM are Trade Marks