Motorola PMNN4434 RMU2040 3.7V Replacement Battery

Motorola RMU2040 / RMU2080 Series — 3.7V Li-ion Replacement Battery (PMNN4434)

This 3.7V, 2200mAh Li-ion battery replaces the PMNN4434, PMNN4434A, and PMNN4434AR packs used in the Motorola RMU2040, RMU2080, RMU2080d, and RMM2050 two-way radios. It slots into the same battery bay and connects to the same gold contact strip as the original. Capacity is rated at 2200mAh (8.14Wh) — matching the factory spec.

• RMU/RMM series platform fit: The RMU2040, RMU2080, RMU2080d, and RMM2050 share a common battery bay geometry, contact layout, and BMS handshake protocol. One pack services the entire line without any adapter or modification.
• Bench tested on actual hardware: We ran this pack through charge acceptance and PTT transmit cycles on the RMU2040 dock. The BMS handled the transmit current spike without tripping, and the charger dock advanced to steady green on a full cycle.
• First insertion on the RMU dock: If the charger dock shows a fault LED on first insertion, remove the battery, wipe the gold contact strip with a dry cloth, and reseat firmly. The RMU platform requires a clean contact cycle to accept the new BMS handshake before charging begins.

Why the RMU2040 cuts out mid-transmission on a new battery

When you press PTT, the radio draws a sharp current spike to drive the RF output stage. A new cell shipped at storage voltage — typically around 3.6V — sits right at the BMS low-voltage threshold. Under that transmit load, the voltage sags just enough to trip the BMS overcurrent protection, cutting the radio off mid-keying. This is not a faulty pack. Run the battery through one full charge cycle on the dock before use and the cell voltage will sit above 4.1V, giving the BMS enough headroom to hold through the transmit spike cleanly.

Bar indicator showing one fewer bar than expected after a full charge

The RMU series uses a simple voltage-threshold bar indicator — each bar maps to a fixed voltage band, not a calculated capacity percentage. A new cell can read one bar short immediately after charge if the dock pulled the charge termination signal slightly early, leaving the cell at 4.05V instead of 4.10V. Remove the battery, reinsert it, and place the radio back on the dock for a second top-up cycle. After that second cycle reaches steady green, the indicator should show the correct full-charge bar count.