"@marioawe ,Thomas, The battery may be faulty, check it again with out charging as you have done that enough, check to see if battery is still holding 3+ volts. Also see if charger is putting out power with your DVOM. Find below a guide below, to show how to tear down the watch so you can carefully remove all connections and clean and reseat them. Use a Qtip/soft rag dampened with 90% Isopropyl Alcohol to clean contacts, work gently not to dislodge delicate components. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
I agree with L Pfaff, normally I'd use a soft toothbrush with the alcohol to clean the contacts. Of course make the the brush is clean before gently cleaning the contacts for the battery and any other you have access to. Good luck buddy.
