About this replacement
Casio PRT-2GP — 3.7V Li-Polymer Replacement Battery (MR11-2286)
This 3.7V, 320mAh lithium-polymer cell replaces the original battery in the Casio PRT-2GP smartwatch. It powers the display, heart rate sensor, GPS, and BLE connectivity. Fit it when the original cell no longer holds a charge or the watch shuts down unexpectedly.
- PRT-2GP platform fit: The PRT-2GP uses a 3.7V Li-Polymer cell with a specific connector orientation and BMS handshake tied to the fuel gauge IC. This cell matches the OEM voltage rail and physical footprint at 32.96 × 28.00 × 4.92mm — no trimming or adapter needed.
- Bench tested on actual hardware: We ran this cell through a full charge cycle on the PRT-2GP platform. The BMS accepted the cell without a low-voltage lockout error, and the fuel gauge IC registered charge state correctly after a complete charge from near-zero.
- Post-swap charging on the PRT-2GP: Place the watch on its magnetic charger immediately after fitting this cell and charge it to 100% before use. The fuel gauge IC on this platform cannot set an accurate reference point without a full charge cycle starting from near-zero — skipping this step causes the display to read 0% or fluctuate wildly.
Why the PRT-2GP battery drains in one day instead of several
The PRT-2GP stacks continuous heart rate monitoring, GPS polling, and BLE syncing on a 320mAh cell. If all three run simultaneously with always-on display enabled, current draw rises sharply and the cell depletes far faster than the rated multi-day estimate. Check your sensor settings — GPS set to continuous rather than interval mode is the single biggest draw. Switching GPS to smart/interval mode and disabling always-on display brings current draw back to the expected range for this cell capacity.
Watch not pairing to phone after battery swap
Removing the battery clears the active BLE session stored in volatile memory — the watch and phone no longer share a valid pairing key. The watch is not faulty; the connection simply needs to be re-established from scratch. On your phone, go to Bluetooth settings, forget the PRT-2GP, then re-pair through the Casio companion app as if setting it up for the first time. The new pairing completes in under a minute once both devices are discoverable.