Very, very happy! I have a TomTom Spark 3 and the only change to these steps for the TomTom Runner is that you are unable to completely disconnect the backing plate completely as it remains joined via a ribbon connector for the optical heart rate sensor.

You still remove the black box vibrator component and then you are able to get in behind the battery to pry it out. Just be careful to not break the ribbon connector.

I ordered a replacement battery from Ali Express “Battery for TomTom Spark 3 Watch New Li-Polymer Polymer Rechargeable Accumulator Pack Replacement 3.7V 280mAh PP332727+Trackable”

https://www.aliexpress.com/item/Battery-...

Also, it wasn’t clear how to disconnect the battery connector… I worked out that it pops out by prying it upwards. The new battery then just snaps back into place.

Thanks!