About this replacement
Motorola CT150 / CT250 / CT450 Series — 7.5V Ni-MH Replacement Battery (PMNN4017)
This is a 7.5V, 2500mAh Ni-MH replacement battery for the Motorola CT150, CT250, CT450, and CT450LS portable two-way radios. It matches OEM part numbers PMNN4017, PMNN4018, PMNN4019AR, PMNN4020, PMNN4021, and PMNN4053. Slot it into any compatible CT-series dock and it charges the same way as the factory pack.
- CT-series platform fit: The CT150 through CT450LS share the same battery bay geometry, contact layout, and 7.5V rail. One pack covers the full lineup because Motorola kept the BMS handshake and connector pinout consistent across this radio family.
- Bench tested on actual hardware: We cycled this pack in a CT250 dock and monitored BMS response through full charge and a PTT transmit load. The BMS held the 7.5V rail steady under transmit current draw and released cleanly at end-of-charge without fault triggering.
- First insertion contact check: 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 CT-series dock requires a clean contact cycle to complete the BMS handshake before it begins charging.
Why the CT450 cuts out mid-transmission on a fresh pack
Ni-MH cells ship at partial storage voltage — typically 1.0–1.1V per cell — not at full charge. When PTT is pressed, transmit current spikes sharply, and cells at storage voltage can sag below the BMS low-voltage cutoff threshold. The radio interprets this as a depleted pack and shuts TX. Running one full charge cycle before field use brings each cell to its rated 1.2V nominal, which gives the BMS enough headroom to handle the transmit surge without tripping.
Bar indicator showing one fewer bar than expected after swapping to this pack
The CT-series radios read battery level using simple voltage thresholds, not a chip that tracks charge history. A new pack at storage voltage sits below the threshold for the top bar, so the indicator reads one bar low even though the pack is not faulty. Charge the battery fully in the dock — cell voltage will climb to approximately 8.4–8.5V at end-of-charge — and the indicator will move to the correct bar level on next power-on.