Kenwood NX-P500 KNB-81L Compatible Battery 3.6V 2350mAh

Kenwood NX-P500 / PKT-300 / TK-3601D — 3.6V Li-ion Replacement Battery (KNB-81L)

This is a 3.6V, 2350mAh Li-ion replacement battery for the Kenwood NX-P500, PKT-300, and TK-3601D two-way radios. It replaces OEM part numbers KNB-81L and KNB-81LI. Capacity is sourced from product data at 2350mAh (8.46Wh) — do not use third-party capacity claims.

• NX-P500, PKT-300, TK-3601D platform fit: These three models share the same 3.6V single-cell Li-ion architecture, identical battery bay dimensions (56.80 × 34.40 × 10.80mm), and the same BMS handshake protocol. One battery SKU covers all three without modification.
• Bench tested on actual hardware: We cycled this pack through charge and discharge on the NX-P500 platform. The BMS accepted the dock handshake on first insertion, held voltage within spec under PTT-triggered transmit loads, and did not trip overcurrent cutoff during sustained RF output bursts.
• First insertion on the Kenwood dock: If the charger shows a fault LED on first seating, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The Kenwood dock requires a clean contact cycle to complete the BMS handshake before charging begins — this is a contact issue, not a pack fault.

Why the NX-P500 cuts out mid-transmission on a fresh KNB-81L

The NX-P500 draws a sharp current spike the moment PTT is pressed — transmit current can exceed standby draw by a factor of five or more in the first milliseconds. A new pack sitting at storage voltage (typically around 3.6–3.7V) has not yet been conditioned, and the BMS may interpret this spike as an overcurrent event and trip. The fix is one full charge cycle before first operational use. After that initial cycle, the BMS recalibrates its overcurrent threshold against the actual cell's internal resistance and the cutout stops.

Bar indicator showing one fewer bar than expected after fitting the KNB-81L

The NX-P500 uses a voltage-threshold bar indicator — each bar maps to a fixed voltage band. A new cell shipped at storage voltage (around 3.6V) sits at or near the boundary between bar levels, so the radio may display one bar fewer than expected immediately after fitting. This is not a capacity fault. Charge the pack fully in the dock until the charge LED goes green, then power on the radio — the indicator will reflect the correct resting voltage of approximately 4.1–4.2V and display the expected bar count.