Motorola batteries require the appropriate sized battery door to ensure compatibility. The thickness of Motorola batteries range from 40, 50, 60, 70, 80 and 90 series. Use the battery model number and the battery door model number to match thickness. For example, a BT50 series battery requires a BT50 series door. Similarly, a BR91 series battery requires a BR90 series door. Be prepared to stay in touch with Motorola batteries and doors.