Nokia THR9 Replacement Battery 3.7V 5200mAh Li-ion

Nokia THR9 Series — 3.7V Li-ion Replacement Battery

This 3.7V, 5200mAh lithium-ion battery replaces the original pack in the Nokia THR9, THR9i, and THR9+ two-way radios. These are compact professional land mobile radios used in commercial and industrial environments. Voltage and capacity match OEM spec exactly — no firmware flag, no indicator error on first power-up.

• THR9, THR9i, and THR9+ compatibility: All three models share the same 3.7V battery rail, physical footprint, and contact arrangement. The BMS handshake protocol is identical across the series, so one pack fits all three without any hardware modification.
• Bench tested on actual hardware: We cycled this pack through transmit loads on the THR9 platform. The BMS held stable across PTT bursts and did not trip on the transmit current spike typical of this radio class.
• Contact strip care on first dock insertion: If the charger shows a fault LED on first insertion, remove the pack, wipe the gold contact strip with a dry cloth, and reseat firmly. The THR9 charging dock requires a clean contact cycle to complete its BMS acceptance handshake before charge current begins.

Why the THR9 cuts out mid-transmission on a new battery

New lithium-ion cells ship at storage voltage — typically around 3.6V to 3.7V, not a full charge. When the THR9 fires a PTT transmission, current draw spikes sharply. If the cell is at storage voltage, that spike can pull the terminal voltage below the BMS overcurrent threshold, triggering a momentary cutoff. The radio reads this as a drop-out, not a low-battery condition. Running one full charge cycle before the first transmission shift eliminates this behaviour entirely.

Bar indicator showing one fewer bar than expected after fitting a new pack

The THR9 uses a voltage-threshold bar indicator — it reads the cell's resting voltage and maps it to a bar count. A new pack at storage voltage sits in the same voltage band as a partially depleted one, so the display shows one or two bars instead of full. This is not a cell fault or a capacity mismatch. Charge the pack fully first; once terminal voltage reaches approximately 4.1V to 4.2V, the indicator will show the correct full-charge bar count.