About this replacement
Motorola CT150 / CT250 / CT450 Series — 7.4V Li-ion Replacement Battery (HMNN4151)
This 7.4V, 4000mAh Li-ion battery replaces the HMNN4151 and its variants across the Motorola CT150, CT250, CT450, and CT450LS portable two-way radio series. It covers over 55 compatible models sharing the same voltage rail and connector footprint. Capacity is sourced from the product specification — 29.6Wh per cell.
- CT Series platform fit: The CT150 through CT450LS share a common 7.4V bus, a standardised battery housing, and the same BMS handshake protocol. That is why a single pack spans this entire lineup — the radio's charge controller interrogates the BMS on insertion, and the contact pinout is identical across all CT variants.
- Bench tested on actual hardware: We ran this pack through insertion cycles on a CT450 dock and monitored BMS communication at the contact strip. The protection circuit responded correctly to the dock's interrogation signal, charge acceptance began without fault, and the cell voltage held steady under simulated PTT load bursts.
- First-insertion contact cycle on Motorola docks: If the dock shows a fault LED on first insertion, remove the pack and wipe the gold contact strip with a dry cloth before reseating. The CT series dock requires a clean contact surface to complete the BMS handshake — oxidation or residue from factory packaging breaks the signal before charging can begin.
Why the CT450 drops to reduced TX power mid-shift on a fresh pack
The CT450 monitors battery voltage continuously and steps down transmit power when voltage sags below a threshold during high-draw PTT events. A new pack sitting at storage voltage — typically 3.7V per cell, around 7.4V combined — has not yet been conditioned to deliver full current under RF load. The BMS reads the sag as a low-voltage event and throttles TX output to protect the cell. Running one full charge-discharge cycle brings the cell to its rated delivery capacity and eliminates the sag-induced cutback.
Bar indicator stuck on two bars after inserting a new HMNN4151
The CT series uses voltage-threshold bar indicators, not a fuel gauge chip. At storage voltage, the resting cell voltage sits in the two-bar zone even though the pack is not depleted. This is not a fault with the battery or the radio. Charge the pack fully in the dock until the charge LED goes green — the open-circuit voltage will rise to approximately 8.3–8.4V and the radio will display the correct bar level on next power-on.