If you ask Garmin support for help they will send you a refurbished replacement watch for aprox 180 euros. On the other hand you can find a new battery or even the rear case with sensors altogether for less than 50 euros. Replacing it is easy. Make sure you have all the tools ( small torx screwdriver set - easy to find on amazon for 10 euros or even better a watch repair set for the same price). Also main the fact that the battery is glued to the rear case; while removing it I had to sacrifice a tweezer, bending it to be able to lift the battery. Don't lose the screws :))
Same goes for all 6 series/pro/solar/sapphire.
