EADS THR850 Compatible Battery BLN-4 3.7V 2000mAh Li-ion

EADS THR850 / THR880 Series — 3.7V Li-ion Replacement Battery (BLN-4)

This is a 3.7V, 2000mAh Li-ion replacement battery for the EADS THR850, THR880, THR880i, and THR880i Light portable two-way radios. It replaces OEM part numbers BLN-4 and BLN-4D. The cell dimensions match the original pack at 72.00 × 33.00 × 15.25mm, so it seats correctly in the battery bay without modification.

• THR850 and THR880 platform fit: These models share the same battery bay dimensions, contact layout, and BMS handshake protocol — which is why one pack covers the full THR8xx line. The BLN-4 connector and pin assignment are identical across all listed variants, including the THR880i Light.
• Bench tested on actual hardware: We cycled this pack under simulated PTT load on the THR880 platform. The BMS held the output rail steady through repeated transmit spikes and tripped correctly on overcurrent — no false lockouts recorded during discharge testing.
• First insertion into the charger dock: If the dock shows a fault LED on the first seating, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The THR850/880 charging platform requires a clean contact cycle to complete the BMS handshake before it will begin charging.

Why the THR850 cuts out mid-transmission on a freshly inserted BLN-4

A new BLN-4 ships at storage voltage — typically around 3.6V, not the 3.7V nominal. When PTT is pressed, the transmit current draw spikes sharply, and the BMS may interpret that voltage dip as an undervoltage condition and cut output. This is not a faulty pack. Run one full charge cycle through the dock before putting the radio into service. After a complete charge, the cell stabilises and the BMS handles transmit spikes without tripping.

Bar indicator showing one fewer bar than expected after fitting a new BLN-4

The THR850 and THR880 use a simple voltage-threshold bar indicator — not a chip that tracks charge history. A new cell at storage voltage reads lower than a fully charged pack, so the radio displays one fewer bar. This is a voltage reading, not a capacity fault. Charge the pack fully before reading the indicator — at 4.2V the display will show the correct bar count.