Kenwood KNB-9A TK-250 Replacement Battery 7.2V 1200mAh

Kenwood TK-250 / TK-255 Series — 7.2V Ni-MH Replacement Battery (KNB-9A)

This is a 7.2V, 1200mAh Ni-MH replacement battery for the Kenwood TK-250, TK-250G, TK-255, and TK-259 portable two-way radios. It replaces OEM part numbers KNB-9A, KNB-11, KNB-11A, KNB-11N, KNB-12, KNB-12A, KNB-18A, and KNB-19A. The pack slots into the same battery bay and connects via the same multi-pin contact strip as the original.

• TK-250 and TK-255 series fit: These models share a common battery bay geometry and 7.2V voltage rail. The BMS handshake protocol and connector pinout are identical across the KNB-9A through KNB-19A family, which is why one pack covers multiple part numbers in this lineup.
• Bench tested on actual hardware: We cycled this pack through transmit loads on the TK-250 platform. The BMS handled the PTT current spike without tripping overcurrent cutoff, and the voltage held stable across sustained RF output.
• First insertion into the dock: If the charger shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat it firmly. The Kenwood dock requires a clean contact cycle to complete the BMS handshake before it begins charging.

Why the TK-250 cuts out mid-transmission on a freshly inserted pack

Ni-MH cells ship at partial storage voltage — typically around 6.0–6.4V for a 7.2V six-cell pack. When PTT is pressed, the transmitter pulls a sharp current spike. If the pack hasn't completed an initial charge cycle, that spike can drag cell voltage below the BMS cutoff threshold momentarily, killing the transmission. This isn't a faulty battery — it's a cell voltage condition. Run one full charge cycle in the Kenwood dock before first use in the field, and the cutout behaviour stops.

Bar indicator showing one fewer bar than expected after swapping in this pack

The TK-250 reads battery status using voltage-threshold detection — it maps resting pack voltage to a bar count on the display. A new Ni-MH pack at storage voltage sits in a lower threshold band than a fully charged one, so the radio correctly reports fewer bars. This is not a capacity or cell defect. Charge the pack fully in the Kenwood dock until the charger LED goes solid green, then reinsert — the indicator will read the correct bar count at or above 7.8V resting voltage.