Nokia THR9 Replacement Battery 3.7V 5700mAh Li-ion

Nokia THR9 / THR9i / THR9+ — 3.7V Li-ion Replacement Battery

This 3.7V, 5700mAh Li-ion cell replaces the original battery in the Nokia THR9, THR9i, and THR9+ professional digital radios. These are secure land mobile radios used in critical workplace communications — a degraded battery in this class of device is not a minor inconvenience. No OEM part number is published for this pack; fit is confirmed by voltage, form factor, and connector type.

• THR9 / THR9i / THR9+ platform fit: All three variants share the same battery bay dimensions and contact configuration. The 3.7V nominal voltage rail and connector pinout are consistent across the series, so one cell covers the full lineup without adapter or modification.
• Bench tested on actual hardware: We cycled this pack through full charge and discharge on the THR9 platform. The BMS handled the transmit current spike on PTT press without tripping into overcurrent lockout, and the protection circuit held within spec across multiple cycles.
• First insertion into the Nokia charger dock: If the dock shows a fault or slow-blink LED on first insertion, remove the pack, wipe the contact strip with a dry cloth, and reseat firmly. The THR9 dock runs a contact handshake to verify BMS state — a micro-oxidation layer on new contacts can break that read on the first attempt.

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

The THR9 manages transmit power in stages. When voltage sags under sustained RF output — particularly during back-to-back PTT use — the radio steps down TX power to protect the circuit rather than cut out entirely. A new cell shipped at storage voltage (typically 3.6–3.7V, not a full 4.1–4.2V charge) has less headroom to absorb that sag. Run the pack through a full charge cycle before the first shift and this behaviour stops. It is a voltage headroom issue, not a cell fault.

Bar indicator showing one fewer bar than expected after fitting this pack

The THR9 reads battery state using voltage thresholds, not a fuel gauge chip. A new cell at storage voltage sits near the boundary between the second and third bar threshold, so the display can read one bar lower than a fully charged pack. This is not a capacity problem — it is where the cell voltage lands after shipping. Charge the pack fully, and the indicator will step up to the correct level once the cell reaches approximately 4.1V.