Hytera PT850 Two-Way Radio Replacement Battery BL1805 3.7V 1800mAh

Hytera PT850 — 3.7V Li-ion Replacement Battery (BL1805)

The BL1805 is a 3.7V, 1800mAh lithium-ion battery for the Hytera PT850 portable two-way radio. It slots directly into the PT850 battery bay and pairs with the radio's charging dock and BMS handshake protocol. Capacity figure is taken from product data — 6.66Wh total energy.

• PT850 platform fit: The PT850 runs a single-cell 3.7V architecture. This battery matches that voltage rail and uses the same contact configuration and BMS signalling the radio expects. No adapter or modification needed.
• Bench tested on actual hardware: We cycled this pack through PTT transmit loads on the PT850 bench unit. The BMS held cutoff at the correct low-voltage threshold and recovered cleanly from a transmit current spike without tripping into lockout.
• First-insertion dock behaviour: If the charging dock shows a fault LED on the first seating, remove the battery, wipe the gold contact strip with a dry cloth, and reseat firmly. The PT850 dock requires a clean contact cycle to complete the BMS handshake before charging begins.

Why the PT850 drops to reduced TX power mid-shift on a new BL1805

A new lithium-ion cell ships at storage voltage — typically 3.6V to 3.7V — not at a full charge state. Under sustained RF output, the PT850 monitors the supply rail and steps down transmit power when voltage sags below its threshold. This is not a faulty battery. Running one full charge cycle through the dock before field use brings the cell to its rated capacity and stabilises the voltage rail under TX load.

Bar indicator showing fewer bars than expected after inserting the BL1805

The PT850 uses a voltage-threshold bar indicator, not a fuel gauge chip. A new cell at storage voltage reads as partially charged, so the radio displays two or three bars instead of four. This is a voltage reading, not a capacity fault. Charge the battery fully in the dock — the indicator will read correctly once the cell reaches 4.1V to 4.2V.