About this replacement
Motorola CT150 / CT250 / CT450 Series — 7.2V Ni-MH Replacement Battery (HMNN4151)
This is a 7.2V 1800mAh Ni-MH replacement battery for the Motorola CT150, CT250, CT450, and CT450LS two-way radios. It replaces OEM part numbers HMNN4151, HMNN4154, PMNN4018, HNN9008, and over 35 additional Motorola part numbers in this family. Capacity is rated at 1800mAh (12.96Wh) — matched to the original specification.
- CT150 / CT250 / CT450 platform fit: These models share the same battery bay geometry, contact alignment, and 7.2V Ni-MH voltage rail across the series. The BMS handshake and connector pitch are consistent across CT-series units, which is why a single battery covers all three.
- Bench tested on actual hardware: We ran this pack through charge and discharge cycles on CT-series hardware. The BMS accepted the charge cycle without fault, and the voltage curve tracked the expected Ni-MH plateau through to cutoff — no mid-cycle lockout, no dock rejection.
- First insertion on a CT-series charger dock: If the dock LED shows a fault on first insertion, remove the battery, wipe the contact strip with a dry cloth, and reseat firmly. The CT-series charger requires a clean contact cycle to initiate the BMS handshake before current delivery begins.
Why the CT450 cuts out mid-transmission on a fresh battery
Pressing PTT draws a sharp current spike — significantly higher than standby draw — as the radio switches to transmit mode. On a Ni-MH pack at storage voltage, that spike can momentarily drag cell voltage below the radio's undervoltage cutoff threshold. The radio interprets this as a depleted pack and shuts TX. One full charge cycle raises resting voltage high enough that the transmit spike no longer triggers the cutoff.
Bar indicator showing one fewer bar than expected after fitting a new pack
The CT-series bar indicator reads voltage thresholds — it does not track charge state electronically. A new Ni-MH cell ships at storage voltage, typically around 6.8–7.0V, which sits below the top-bar threshold of approximately 7.2V. The radio displays one or two bars even though the pack is not depleted. After a full charge cycle brings resting voltage up to spec, the indicator will read correctly.