About this replacement
Motorola APX-2000 / APX-3000 Series — 7.4V Li-ion Replacement Battery (NNTN8128A)
This is a 7.4V, 2300mAh Li-ion battery for the Motorola APX-2000 and APX-3000 portable two-way radios. It replaces OEM part numbers NNTN8128A, NNTN8128C, PMNN4406AR, PMNN4424, and several variants. APX-series radios are P25-capable land mobile radios used by public safety and enterprise teams on extended operational shifts.
- APX-2000 and APX-3000 compatibility: Both models share the same battery bay geometry, contact pin layout, and BMS handshake protocol. The voltage rail is identical at 7.4V nominal, so one battery SKU covers both platforms without modification.
- Bench tested on actual hardware: We ran this pack through full charge and transmit-load cycles on APX-series hardware. The BMS negotiated correctly with the radio's power management circuit, and the protection circuit responded properly to simulated PTT current spikes without tripping into lockout.
- First insertion into the charger dock: If the dock LED flashes fault on first insertion, remove the battery, wipe the gold contact strip with a dry cloth, and reseat firmly. The APX charger dock requires a clean contact cycle to accept the new BMS handshake before it begins the charge sequence.
Why the APX-2000 cuts out mid-transmission on a new battery
The APX-2000 draws a significant current surge the instant PTT is pressed — RF output plus audio amplification hit the battery simultaneously. If the new pack arrived at storage voltage (typically around 3.7–3.8V per cell), the BMS may interpret the transmit-load spike as an overcurrent event and trip the protection circuit before the radio can sustain the transmission. This is not a faulty battery. Charge the pack fully to 8.4V before the first use and the BMS will operate within its normal window during PTT events.
Bar indicator showing one fewer bar than expected on a fresh pack
The APX series reads battery state through simple voltage-threshold levels — each bar corresponds to a voltage band. A new cell shipped at storage voltage sits below the top threshold, so the radio displays one bar fewer than a fully charged pack even though the cell is not depleted. This is expected behaviour at storage voltage, not a capacity defect. Charge the battery fully before reading the bar indicator — once the pack reaches 8.4V, the top bar will register correctly.