KNB-55L Replacement Battery for Kenwood TK-2140 7.4V 3300mAh

Kenwood TK-2140 / TK-3140 Series — 7.4V Li-ion Replacement Battery (KNB-55L)

This 7.4V Li-ion battery replaces OEM part numbers KNB-55L, KNB-35L, KNB-57L, KNB-24L, KNB-56N, KNB-78L, and KNB-79LC at 3300mAh capacity. It fits the Kenwood TK-2140, TK-3140, TK-2148, TK-3148, and over 20 additional TK-series portables. The pack slots into the same housing footprint as the original and connects to the same charging dock contacts.

• TK-2140 / TK-3140 series compatibility: These models share a common 7.4V battery rail, identical latch geometry, and the same BMS handshake protocol across the sub-series — one pack covers the full range without any adapter or modification.
• Bench tested on actual hardware: We ran this pack through full charge and transmit cycles on a TK-2140 dock. The BMS accepted the charger handshake on first insertion, held voltage above the radio's low-battery cutoff threshold throughout sustained PTT cycles, and did not trip overcurrent protection during the transmit surge.
• First insertion on a Kenwood dock: If the dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The TK-series dock requires a clean contact cycle to complete the BMS handshake before it begins charging.

Why the TK-2140 cuts out mid-transmission on a new battery

New Li-ion cells ship at storage voltage — typically 3.6–3.7V per cell, not full charge. When the TK-2140 draws transmit current at storage voltage, the cell voltage can sag below the BMS's overcurrent cutoff threshold, causing the radio to drop out mid-PTT. This is not a faulty pack. Charge the battery fully before first field use — the dock needs to bring both cells to 4.2V before the pack handles sustained RF output without voltage collapse.

Bar indicator showing one fewer bar than expected after fitting the KNB-55L

The TK-series radio reads battery state from cell voltage using fixed voltage thresholds — it does not recalibrate when a new pack is inserted. A new pack at storage voltage reads as partially depleted against those thresholds, so the indicator shows one or two bars instead of full. Run the pack through a complete charge cycle in the Kenwood dock until the charge LED goes green, then reinsert into the radio. At 8.4V full charge, the indicator will return to the correct bar count.