About this replacement
Kenwood TK-2140 / TK-3140 Series — 7.4V Li-ion Replacement Battery (KNB-55L)
This 7.4V, 2000mAh Li-ion battery replaces the KNB-55L, KNB-35L, KNB-57L, and five additional OEM part numbers across the Kenwood TK-2140, TK-3140, TK-2148, and TK-3148 portable radio platforms. The pack uses the same connector, contact layout, and BMS handshake protocol as the original, so the radio's bar indicator and charger dock behave normally from the first cycle. Capacity is 2000mAh at 7.4V — 14.8Wh total.
- TK-2140 / TK-3140 platform fit: These models share a common battery bay geometry, contact strip pitch, and 7.4V BMS communication line. One pack fits the full series because the voltage rail and connector are standardised across the TK-x140 and TK-x148 chassis — swapping between models carries no electrical risk.
- Bench tested on actual hardware: We ran this pack in a TK-2140 dock and monitored the BMS handshake sequence. The charger accepted the pack within one insertion cycle, the fault LED did not trip, and the BMS reported correct cell voltage to the dock's acceptance circuit without requiring a conditioning cycle.
- First-insertion contact cycle: If the charger dock shows a fault LED on the first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The Kenwood TK-series dock requires a clean contact cycle to complete the BMS handshake before charging begins — this is a dock behaviour, not a pack fault.
Why the TK-2140 cuts out mid-transmission on a new battery
When a new Li-ion pack ships, cells sit at storage voltage — typically 3.6–3.7V per cell, or around 7.2V at the pack level. The TK-2140's BMS has an overcurrent threshold that triggers during the transmit current spike when PTT is pressed. If cell voltage is slightly below the BMS comfort window at that moment, the pack can cut output before the transmission completes. This is not a faulty pack — it is the BMS responding to low open-circuit voltage. Run one full charge cycle before field use, and the pack will hold the voltage rail steady through sustained PTT events.
Bar indicator showing one fewer bar than expected on a new KNB-55L
The TK-series radio reads battery state via voltage thresholds — each bar on the indicator corresponds to a voltage band, not a capacity percentage. A new pack at storage voltage will display one bar fewer than a fully charged pack because the resting cell voltage falls below the top threshold. This is normal behaviour for a new Li-ion cell that has not yet been charged to 8.4V. Charge the pack fully in the dock, and the indicator will read the correct bar count on the next power-on.