EADS THR9 Replacement Battery BLN-5i 3.7V 5200mAh

EADS THR9 / THR9i Series — 3.7V Li-ion Replacement Battery (BLN-5i / BLN-6)

This 3.7V, 5200mAh Li-ion battery replaces the BLN-5i and BLN-6 packs used in the EADS THR9, THR9i, and THR9 C-30 portable radios. These are TETRA-capable land mobile radios used in professional and public safety communications. Voltage and capacity match the original spec exactly — 3.7V nominal, 19.24Wh.

• THR9 / THR9i / THR9 C-30 platform fit: All three models share the same battery bay geometry, contact layout, and BMS handshake protocol — which is why a single cell covers the whole series. The BLN-5i and BLN-6 are interchangeable across these variants.
• Bench tested on actual hardware: We ran this pack through a full charge-discharge cycle on the THR9 platform. The BMS responded correctly to charge termination, and transmit current draw during PTT did not trigger overcurrent cutoff at any point in the cycle.
• First insertion into the THR9 dock: If the dock shows a fault LED on first insertion, remove the battery and wipe the gold contact strip with a dry cloth before reseating. The THR9 charging dock requires a clean contact cycle to complete the BMS handshake — a single wipe and firm reseat clears this in most cases.

Why the THR9 drops to reduced TX power mid-shift on a new battery

TETRA radios like the THR9 draw a sharp current spike at the start of each transmission slot. If the cell is at storage voltage rather than a full charge — common with new stock — the voltage sag under that spike can push below the radio's TX power threshold. The radio doesn't shut off; it steps down output power to stay within the voltage window. A full charge cycle before first use brings the cell to 4.2V and eliminates this sag margin problem.

Bar indicator shows one fewer bar than expected after fitting new BLN-5i

The THR9 uses a voltage-threshold bar indicator — it reads the cell voltage and maps it to a bar level, with no fuel gauge IC involved. A new cell shipped at storage voltage (typically 3.6–3.8V) will display one bar fewer than a fully charged pack. This is not a cell fault. Charge the battery fully in the dock until the indicator goes green, then reinsert — the bar count will reflect the correct 4.2V terminal voltage.