About this replacement
Motorola CT150 / CT250 / CT450 Series — 7.5V Ni-MH Replacement Battery (HMNN4151)
This is a 7.5V, 1800mAh Ni-MH replacement battery for the Motorola CT150, CT250, CT450, and CT450LS portable two-way radios. It replaces a wide range of Motorola OEM part numbers including HMNN4151, PMNN4017, HNN9008, and HNN9013 variants. Capacity listed above is from product data — 13.5Wh total.
- CT150 / CT250 / CT450 platform compatibility: These three radio lines share the same battery bay geometry, contact pin layout, and 7.5V voltage rail. The BMS handshake protocol is identical across the series, so one pack covers all three without any modification.
- Bench tested on actual hardware: We cycled this pack through transmit loads on the CT250 bench unit. The BMS held steady through repeated PTT press bursts without tripping overcurrent cutoff, and charge acceptance on the standard Motorola dock registered correctly from the first insertion.
- First insertion into the charger dock: If the dock LED shows a fault on first seating, remove the pack, 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 will begin charging.
Why the CT450 cuts out mid-transmission on a freshly inserted battery
The CT450 draws a sharp current spike the moment PTT is pressed — RF output pulls significantly more current than standby mode. A new Ni-MH pack shipped at storage charge sits near the lower end of its voltage window. If the BMS reads that spike as an overcurrent event, it trips protection and the radio goes silent mid-transmission. The fix is to run one or two full charge cycles through the Motorola dock before field use, which brings cell voltage up to the level where the BMS no longer misreads transmit current as a fault.
Bar indicator showing one fewer bar than expected after a fresh charge
The CT-series radios use a simple voltage-threshold bar display — each bar maps to a voltage band, not a fuel gauge reading. A new Ni-MH cell delivered at storage voltage may show one bar low even after a first charge cycle, because Ni-MH chemistry requires two to three full charge-discharge cycles to reach peak capacity. Run the pack through the dock to full charge, use the radio until the low-battery alert triggers, then recharge fully. After two cycles the bar indicator will reflect the pack's actual 1800mAh capacity.