@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.
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