I had the exact same issue on a 6 months old watch! My battery life was around 2 days as with most say with a moderate use of occasional GPS, few sports apps beside full time connection. then came one dreadful morning I woke up to a dead battery. Not suspecting much of it, I recharged again only to realize after 5-7 hours that battery evaporates (15-18% per hour). Unlike you, I had no update, did not change no setting, nothing - problem came out of nowhere. The weird thing was that It did not matter If I turned on Power Saving mode or reset n number of times. All the same, battery gone in a few hours. Seeing that and similar issues online, I realized this is not something can be resolved. I was really pissed such a silly fault product can make its way to market with no way of knowing before hand. I have a ton of Samsung products from household items to gear 360 I was very happy with, but this was a real deal breaker. I took the watch to service, obviously under warranty and was very surprised the quality of service provided. They took the watch beg it, took my phone number and 3 days later issue was fixed. I see that they had to replace motherboard and battery which tells me something was fundamentally went wrong with the watch. It looks ok now but I must tell you that when almost brand new product that you really like suddenly becomes useless is quite a trust shaker. I will continue to opt for Samsung however I hope they clear such out of content issues promptly.
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