TomTom GPS-9821X Replacement Battery 3.7V 650mAh Q6000021

TomTom GPS-9821X — 3.7V Li-ion Replacement Battery (Q6000021)

This 3.7V, 650mAh Li-ion cell replaces part number Q6000021 in the TomTom GPS-9821X portable navigator. It restores power to the unit when the original cell can no longer hold a charge or causes unexpected shutdowns. Dimensions are 60.00 x 30.50 x 4.50mm — measure your original before fitting if you are unsure.

• GPS-9821X and GPS-9821X PDA/Handheld fit: Both model variants run the same 3.7V single-cell architecture with the same connector pinout and BMS communication protocol, so one cell covers both listings.
• Bench tested on actual hardware: We ran the Q6000021 replacement through full charge and discharge cycles on the GPS-9821X platform. The BMS accepted the cell without fault flags, and voltage at full charge held at 4.2V within spec.
• Cold-start satellite acquisition after swap: After fitting this cell, power the GPS fully on outdoors before driving. A full power interruption forces a cold start — first satellite fix takes 5–10 minutes. Subsequent warm starts drop to under a minute once almanac data is cached.

GPS-9821X shutting off without warning at low battery

The GPS-9821X uses a voltage-threshold system to gauge remaining charge. After a new cell is fitted, the device's fuel gauge is uncalibrated against the new cell's discharge curve. This means the low-battery warning indicator and the actual cutoff threshold fall out of sync — the unit can shut off abruptly before the visual warning fires. Run two full charge-to-discharge cycles to allow the threshold to recalibrate. Shutoffs should stabilise once the device has mapped the new cell's curve down to the 3.0V cutoff floor.

Saved routes and POIs missing after battery replacement

Some TomTom GPS-9821X units store active route data and recent POIs in battery-backed volatile RAM rather than flash. A full power removal — which battery replacement causes — clears that RAM entirely. Saved favourites stored in non-volatile flash survive the swap, but unsaved routes and recent destinations will not. Export any routes you need to keep via TomTom HOME or MyDrive before removing the old cell.