Motorola NNTN8359 DGP8550E Replacement Battery 7.4V 2000mAh

Motorola DGP8550E / DP4000ex Series — 7.4V Li-ion Replacement Battery (NNTN8359)

This is a 7.4V, 2000mAh Li-ion replacement battery for the Motorola DGP8550E, DP4000ex, DP4401Ex, and DP4401ex ATEX series portable two-way radios. It replaces OEM part numbers NNTN8359, NNTN8359A, and NNTN8359C. The cell pack matches the original voltage rail and BMS handshake profile required by the Motorola charging dock ecosystem.

• DGP8550E and DP4000ex platform fit: These models share the same battery bay geometry, 7.4V power rail, and BMS communication protocol. One cell pack covers the full range — the BMS on each radio expects the same handshake signature at insertion, so the dock accepts this pack the same way it accepts the OEM unit.
• Bench tested on actual hardware: We ran this pack on a DP4401Ex dock and monitored the BMS handshake cycle at insertion. The protection circuit responded correctly to the transmit-current spike during PTT hold and did not trigger an overcurrent cutoff under sustained RF output load.
• First insertion contact cycle: If the charger dock shows a fault LED on first insertion, remove the battery and wipe the gold contact strip with a dry cloth, then reseat firmly. The Motorola dock requires a clean contact surface to complete the BMS handshake before it will begin charging — a smudged contact is enough to stall the cycle.

Why the DGP8550E drops to reduced TX power mid-shift on a new pack

New Li-ion cells ship at storage voltage — typically 3.7V per cell, putting the pack around 7.4V total at rest. Under sustained RF output, the voltage sags faster from storage charge than from a fully conditioned cell. The radio's power management circuit interprets the sag as a low-battery condition and steps the transmitter down to protect the final amplifier stage. Run one full charge cycle before the first operational shift and the sag behaviour normalises.

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

The DGP8550E uses voltage-threshold stepping to drive the bar indicator — it is not a fuel gauge chip reading cell chemistry directly. A new pack at storage voltage will sit at a threshold that maps to one bar fewer than full. This is not a capacity fault. Charge the pack completely in the Motorola dock until the LED goes solid green, then reinsert — the indicator will read the correct threshold and display the expected full-charge bar level.