About this replacement
Midland 777 / PMR446+ — 3.7V Li-ion Replacement Battery (PB-777)
The PB-777 is a 3.7V 650mAh Li-ion battery for the Midland 777 and PMR446+ handheld two-way radios. It slides into the same battery compartment as the original pack and uses the same contact layout. Dimensions are 50.00 × 34.60 × 5.20mm — confirming physical fit before ordering is straightforward.
- 777 and PMR446+ platform fit: Both models share the same battery bay geometry, contact pin arrangement, and 3.7V voltage rail. A single pack covers both devices with no adapter required.
- Bench tested on actual hardware: We cycled this pack through full charge and discharge runs on a 777 unit. The BMS handled the transmit current spike on PTT press without tripping, and charge termination triggered cleanly at rated voltage.
- First insertion contact check: If the charger shows a fault or no-charge state on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The Midland dock needs a clean contact cycle to complete the BMS handshake before charging begins.
Why the Midland 777 bar indicator reads low on a new PB-777
New Li-ion cells ship at storage voltage — typically around 3.6–3.7V — not at full charge. The 777 uses a simple voltage-threshold system to drive the bar indicator, so a cell sitting at storage voltage will display one or two bars even though the pack is not faulty. Insert the battery, place it in the charger, and run a full charge cycle before reading the bar level. Once the pack reaches its upper voltage threshold, the indicator will reflect actual charge state.
Radio cuts out mid-transmission after a PTT press
Transmitting draws a sharp current spike — well above standby draw — in the first milliseconds after PTT is pressed. If the cell voltage sags far enough under that load, the BMS trips an overcurrent cutoff and the radio drops out. This is more likely with an aged or deeply discharged pack where internal resistance has climbed. Charge the PB-777 fully before use and confirm resting voltage is at or above 3.7V before putting the radio back into service.