I've got another data point to add here. I also updated my T-Mobile Gear S3 Frontier to Tizen 3.0 a couple months ago. After doing a factory reset, turning off continuous heart monitoring, etc., I still did see a hit to my battery, though nothing catastrophic, i.e. it's about 4.5-5% drain per hour during the day, and 2% per hour if I wear it to bed. It's enough to get through a 24 hour cycle, but barely. I usually charge my watch for about half an hour in the middle of the day, and once again in the afternoon after I go jogging (Samsung Health is a big drain), but if I didn't then I imagine I'd be at 5%-10% at the end of 24 hours.
It's hard to tell how much of this is due to Tizen 3.0, because I've owned this watch for two years and the battery life was getting progressively worse even before the upgrade. For reference, out of the box my watch was discharging at about 2%/hour during the day, and about 0.5%/hour at night. Right before I upgraded, I was getting about 3%/hour.
I'm going to take my watch to a watch repair shop this weekend or next week to get a new battery (apparently, some normal watch repair places are now able to replace smartwatch batteries). I'll report back a couple days after I get this done to let you guys know what kind of battery life I'm seeing.
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