About this replacement
T-Mobile SyncUP Kids — 3.85V Li-Polymer Replacement Battery (P0963)
This 3.85V, 490mAh Li-Polymer cell replaces the original battery in the T-Mobile SyncUP Kids GPS smartwatch. It fits the P0963 battery slot directly. Use it when the watch no longer holds charge or fails to power on after a full charge.
- SyncUP Kids platform fit: The SyncUP Kids watch runs GPS tracking, LTE calling, and BLE pairing from a single cell. The P0963 footprint — 29.80 × 25.10 × 5.80mm — matches the battery bay exactly, and the voltage rail aligns with the watch's power management IC so no adapter or modification is needed.
- Bench tested on actual hardware: We cycled this cell through the SyncUP Kids charging circuit and confirmed the BMS accepted the charge handshake without fault codes. The protection circuit tripped correctly at undervoltage during discharge, then recovered on reconnection to the charger.
- Fuel gauge re-initialisation after swap: Place the watch on its magnetic charger immediately after fitting this cell and charge it to 100% before first use. The fuel gauge IC on this platform loses its state of charge reference when the cell is removed — it cannot calibrate the percentage readout without a full charge cycle from near-zero after a swap.
Why the SyncUP Kids watch shows 0% right after a new battery is fitted
The fuel gauge IC stores its capacity reference in volatile memory. When the original cell is removed, that reference is wiped. The IC then reads the new cell's open-circuit voltage but cannot map it to a percentage without a known baseline. Charging to 100% from a low state gives the IC the full sweep it needs to reset its internal model. Until that cycle completes, the display will show 0% or refuse to boot past the charging screen.
Magnetic charge contacts not connecting after reassembly
If the watch does not register on the charger after the battery swap, the charge contact pads on the watch case have likely shifted during reassembly. Press the watch face firmly onto the magnetic charger and rotate it slightly — the magnets will pull it into alignment when the contacts are close enough. If the watch still does not respond, check that the rear cover is fully seated and flush; a raised edge can hold the contact pads a fraction of a millimetre above the charger pins. A correctly docked watch will show the charging animation within five seconds of placement.