About this replacement
Kirisun PT-6500 / PT-6800 — 7.4V Li-ion Replacement Battery (KB-36C)
The KB-36C is a 7.4V, 1800mAh Li-ion battery for the Kirisun PT-6500 and PT-6800 portable two-way radios. These are professional VHF transceivers used in public safety, transport, and commercial operations. This replacement restores full transmit power when the original pack no longer holds voltage under load.
- PT-6500 and PT-6800 compatibility: Both models share the same battery bay dimensions, connector pinout, and BMS handshake protocol. The KB-36C slot fits both without modification — the 7.4V nominal rail and two-pin data line are identical across the pair.
- Bench tested on actual hardware: We cycled this pack through full charge and transmit-load discharge on the PT-6500. The BMS handled the PTT current spike without tripping, and voltage held above 7.0V through sustained TX output.
- First insertion into the charger dock: If the dock LED shows a fault on first seat, remove the pack and wipe the contact strip with a dry cloth. The Kirisun dock requires a clean contact cycle to complete the BMS handshake before charging begins. Reseat firmly and the fault clears.
PT-6500 cutting out mid-transmission on a new KB-36C
A new Li-ion pack ships at storage voltage — typically 3.6–3.7V per cell, not full charge. The PT-6500 BMS monitors cell voltage under TX load, and if the pack hasn't been fully charged before first use, the voltage sag during a PTT burst can hit the BMS undervoltage threshold. The radio cuts audio or drops carrier as a protective response, not a fault with the pack itself. Charge the KB-36C to full before the first transmission cycle and the cutout stops.
Bar indicator showing one fewer bar than expected on a fresh KB-36C
The PT-6500 uses a simple voltage-threshold bar indicator — each bar maps to a voltage band, not a capacity percentage. A new pack at storage voltage sits in a lower band, so the radio displays one or two bars even though the cell is not depleted. This is not a defective cell or a calibration issue. Run a full charge cycle first; the bar display will reflect the correct resting voltage once the pack reaches 8.3–8.4V.