About this replacement
Kenwood NX-220 / NX-320 Series — 7.4V Li-ion Replacement Battery (KNB-57L)
This 7.4V, 2000mAh Li-ion battery replaces the KNB-24L, KNB-35L, KNB-55L, KNB-56N, KNB-57L, KNB-78L, and KNB-79LC OEM packs. It fits the Kenwood NX-220, NX-320, NX-3220, NX-3320, and over 20 additional NX-series and NEXEDGE radios. Same voltage rail, same connector footprint, same BMS handshake protocol as the factory pack.
- NX-220 / NX-320 / NX-3220 / NX-3320 platform fit: These four radios share the same battery bay dimensions, 7.4V power rail, and BMS communication pins. One pack covers all four because the dock charge circuit and transmit draw spec are identical across the group.
- Bench tested on actual hardware: We ran this pack through PTT transmit cycles on the NX-320 platform. The BMS handled the transmit current spike without tripping overcurrent cutoff, and the dock accepted the BMS handshake on the first insertion cycle.
- First-insertion contact check: If the charger dock shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The Kenwood NEXEDGE dock requires a clean contact cycle to register the new BMS before it begins charging — this is not a faulty pack.
Why the NX-220 cuts out mid-transmission on a freshly inserted pack
The NX-220 transmit circuit draws a sharp current spike the moment PTT is pressed. If the battery BMS has not completed its handshake with the radio's protection circuit, that spike can trip the BMS overcurrent threshold and cut the transmission instantly. This is more likely with a new pack sitting at storage voltage — roughly 3.7V per cell — rather than a fully charged one. Charge the pack to full in the dock before the first shift and the BMS trip threshold resets to its normal operating window.
Bar indicator showing one fewer bar than expected after a full dock charge
The NX-series bar indicator reads voltage thresholds, not a fuel gauge chip. A new cell shipped at storage voltage can show one bar below full even after the dock light goes green, because the first charge cycle does not always bring the cell to peak resting voltage. Run one full discharge-to-cutoff followed by a complete dock charge. After that cycle, the resting voltage stabilises above 8.2V and the bar indicator reads correctly.