About this replacement
Motorola MTH800 / MTH650 Series — 3.7V Li-ion Replacement Battery (NNTN6923A)
This 3.7V 1700mAh Li-ion battery replaces the original pack on the Motorola MTH800, MTH650, DTR550, and DTR650 portable radios. It matches the OEM voltage rail, connector pinout, and BMS handshake required by the Motorola charging dock. Capacity is 1700mAh (6.29Wh), consistent with the standard-series pack.
- MTH800 and MTH650 platform fit: These models share the same battery bay, connector, and dock communication protocol. One pack covers both radio lines without any adapter or modification.
- Bench tested on actual hardware: We cycled this pack through full charge and discharge on the MTH800 dock. The BMS accepted the handshake correctly, the dock progressed to ready status, and no fault LED triggered during the charge cycle.
- First dock insertion on the MTH800: If the dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The MTH800 dock requires a clean contact cycle to complete the BMS handshake before charging will begin.
Why the MTH800 cuts out mid-transmission on a new battery
The MTH800 draws a sharp current spike the moment PTT is pressed — transmit current can briefly exceed 1.5A on a fresh cell sitting at storage voltage near 3.6V. If the BMS reads this spike as an overcurrent event, it will trip the protection circuit and cut audio output mid-transmission. This is not a defective pack. Fully charge the battery before its first transmission use; once the cell reaches 4.1–4.2V, the BMS headroom is sufficient to pass the PTT current spike without tripping.
Bar indicator showing one fewer bar than expected after fitting this pack
The MTH800 uses voltage-threshold bar indicators — each bar maps to a specific voltage band, not a fuel gauge chip. A new pack shipped at storage voltage (around 3.6V) will sit in the lower threshold band and display one fewer bar than a fully charged cell. This is not a capacity fault. Place the pack in the dock for a full charge cycle; once cell voltage reaches approximately 4.1V, the bar indicator will reflect the correct charge level.