Airbus THR9 Replacement Battery BLN-5i 3.7V 2300mAh

Airbus THR9 Series — 3.7V Li-ion Replacement Battery (BLN-5i / BLN-6)

This 3.7V, 2300mAh Li-ion battery replaces the BLN-5i and BLN-6 packs used in the Airbus THR9, THR9i, THR9 C-30, and THR9 Ex portable radios. These radios operate in aviation, emergency services, and industrial environments where a dead pack mid-shift is not an option. Dimensions match the original at 97.46 × 53.62 × 14.96mm, so the pack seats flush in the radio body and charger dock without modification.

• THR9 series fit — all four variants: The THR9, THR9i, THR9 C-30, and THR9 Ex share the same battery bay geometry, contact layout, and BMS handshake protocol. One pack covers all four models because the voltage rail and connector position did not change across the series.
• Bench tested on actual hardware: We ran this pack through charge and discharge cycles on the THR9 platform. The BMS accepted the dock handshake cleanly, held voltage under PTT transmit load, and triggered overcurrent protection at the correct threshold without nuisance tripping during normal keying.
• First insertion into the dock: 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 THR9 dock requires a clean contact cycle to complete the BMS handshake before charging begins — a single reseating usually clears it.

Why the THR9 drops to reduced TX power during sustained RF output

The THR9 draws a sharp current spike each time the PTT key is pressed, and sustained transmission at full power adds thermal and voltage load on top of that. If the pack voltage sags below the radio's internal threshold during a long transmission, the firmware steps down TX power to protect the final stage amplifier. A new cell shipped at storage voltage — typically around 3.6–3.7V — is more susceptible to this sag than a fully charged pack. Charge the battery fully before a demanding shift; a pack at 4.1–4.2V handles the sustained RF draw without triggering the power reduction step.

Bar indicator showing one fewer bar than expected straight out of the box

Replacement packs ship at storage voltage, not full charge, so the THR9's voltage-threshold bar indicator will read low on first power-up — this is normal, not a fault with the cell. The radio maps voltage levels directly to bar segments, so a pack sitting at 3.6V will show one or two bars rather than a full display. A complete charge cycle in the dock will bring the cell to 4.1–4.2V, and the indicator will show the expected full reading. If the bar count does not increase after a full charge, check dock contact cleanliness before assuming a cell problem.