Amazfit A2169 Stratos Replacement Battery 3.87V 500mAh

Amazfit A2169 / T-Rex 2 — 3.87V Li-Polymer Replacement Battery (PL572428)

This is a 3.87V 500mAh Li-Polymer cell (PL572428) for the Amazfit Stratos smartwatch and T-Rex 2 series. It fits the A2169 and A2170 chassis and restores power to watches that no longer hold a charge or fail to turn on. Capacity is rated at 500mAh (1.94Wh) — exactly as the original cell.

• A2169, A2170 and T-Rex 2 compatibility: All three models share the same PL572428 cell footprint, connector pitch, and 3.87V nominal voltage rail. The BMS on each platform communicates with the same fuel gauge IC, so a single replacement cell covers the group without modification.
• Bench tested on actual hardware: We cycled this cell through charge and discharge on a T-Rex 2 unit. The BMS accepted the new cell without fault flags, and the fuel gauge completed its calibration pass after a full charge cycle from near-zero.
• Post-swap charge protocol for Amazfit fuel gauge calibration: After fitting the new cell, place the watch on its magnetic charger immediately and charge to 100% before use. The fuel gauge IC on this platform loses its reference point when power is removed during a swap — skipping this step causes the gauge to report incorrect percentages for several days.

Why the T-Rex 2 reports wildly incorrect battery percentages after a cell swap

The T-Rex 2 uses a coulomb-counting fuel gauge IC that tracks charge by measuring current in and out of the cell over time. When the old cell is disconnected, the IC loses its accumulated reference data entirely. It then tries to estimate state-of-charge on the new cell using stale or zeroed parameters, which produces jumpy or stuck readings — often showing 0%, 100%, or a fixed number that doesn't move. The fix is a full charge to 4.35V followed by a normal discharge cycle, which gives the IC enough data to rebuild an accurate model of the new cell's capacity curve.

Watch not pairing with the Amazfit app after battery replacement

Removing the battery kills the BLE session stored in the watch's memory, and the phone-side Amazfit app retains the old device record without knowing the watch rebooted cold. When the watch powers back up, it broadcasts as a new session, but the app tries to reconnect to the old one and fails silently. Go into the Amazfit app, remove the existing device entry, then re-add the watch from scratch using the pairing flow. Make sure the watch is showing the Bluetooth icon on screen before initiating the pairing scan.