About this replacement
TomTom Runner Cardio / Spark — 3.8V Li-Polymer Replacement Battery (AHB322028)
This is a 3.8V, 190mAh lithium-polymer cell for the TomTom Runner Cardio, Runner, and Spark 8rs00 smartwatches. It replaces part number AHB322028 and fits the same 27.40 × 18.14 × 2.50mm cavity as the original. Swap it when the watch no longer holds charge through a full training session.
- Runner Cardio, Runner, and Spark 8rs00 fit: All three models share the same AHB322028 cell format, connector pinout, and BMS handshake protocol. One replacement cell covers the entire group without modification.
- Bench tested on actual hardware: We cycled this cell through charge and discharge on a Runner Cardio unit. The BMS accepted the new cell without error flags, and the fuel gauge IC registered capacity correctly after a full charge cycle.
- First charge after swap: After fitting this cell, place the watch on its magnetic charger immediately and charge to 100% before use. The fuel gauge IC on this platform loses its calibration reference when the cell is removed — it cannot reset without a full charge cycle from near-zero.
Why the Runner Cardio shows 0% immediately after a battery swap
The TomTom Runner Cardio uses a fuel gauge IC to track state-of-charge, not a simple voltage read. When the cell is disconnected, that IC loses its reference point entirely. It comes back up reading zero because it has no history on the new cell. Placing the watch on its charger and running a full charge cycle to 100% gives the IC a fixed upper boundary to calibrate from. After one complete charge, the percentage display will behave normally.
New battery draining in under a day instead of the expected multi-day life
A 190mAh cell is a small reserve, and continuous optical heart rate monitoring pulls a consistent current draw that adds up fast. If the Runner Cardio is set to always-on heart rate tracking, the sensor alone can flatten the cell well before a 24-hour mark. Check the HR monitoring mode in the TomTom MySports app and switch from continuous to activity-only if all-day battery life is the priority. Also confirm the watch face backlight timeout is set to its shortest option, as that display draw compounds quickly on a cell this size.