FTN6574 Motorola MTP850 Replacement Battery 3.7V 2200mAh

Motorola MTP850 / CEP400 Series — 3.7V Li-ion Replacement Battery (FTN6574)

This is a 3.7V, 2200mAh Li-ion replacement battery for the Motorola MTP850, MTP800, CEP400, and PTX850 portable digital radios. It cross-references OEM part numbers FTN6574, FTN6574A, FTN6574BC, PMNN4351, PMNN6074, and related variants. Drop-in fit with the original battery bay — no adapter or modification needed.

• MTP850 / CEP400 platform compatibility: These models share the same battery bay geometry, contact pin layout, and BMS handshake protocol. The 3.7V nominal rail is consistent across the MTP800 and PTX850 as well, so one pack covers the full group without voltage mismatch at the radio's power management circuit.
• Bench tested on actual hardware: We ran this pack through a full charge cycle on the Motorola multi-unit charger dock. The BMS negotiated correctly on first insertion, accepted charge without fault, and held the rated voltage at rest after a full cycle.
• First insertion into the charger dock: If the dock LED flashes amber or shows a fault on the first seating, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The MTP850 platform requires a clean contact cycle for the BMS to complete its handshake before charging begins.

Why the MTP850 cuts out mid-transmission on a new battery

When PTT is pressed on the MTP850, transmit current spikes sharply — often two to three times the standby draw. A new pack sitting at storage voltage (typically around 3.6–3.7V) has not yet been fully cycled, so internal resistance is slightly elevated. Under that spike, the BMS may interpret the voltage drop as an overcurrent event and trip the protection circuit, cutting audio mid-transmission. One full charge-discharge cycle brings cell impedance down and the cutout stops.

Bar indicator showing one fewer bar than expected after fitting this pack

The MTP850 uses a voltage-threshold bar indicator — it reads bars based on resting cell voltage, not a fuel gauge chip. A new cell shipped at storage voltage sits lower than a freshly charged pack, so the radio displays one fewer bar than expected straight out of the packaging. This is not a capacity fault. Charge the pack fully in the dock before first use and the indicator will read correctly at 3.7V nominal.