I wasn't doing anything but typing at work and it popped off. you can see the battery swelling so that was obviously the issue. I purchased this one when best buy was having the crazy sale on the SS models in late 2016. I bought one for me and my wife. i also purchased apple care+ which expired about 4 months ago. her's was replaced when the back fell off - they replaced it with the same series 0 with no issues. I quickly called Apple to discuss my options on this. the rep was helpful and offered $79 for a battery replacement but said they'll just replace the whole watch and not just the battery for $79. I know there was an extension on a repair program for the original apple watches on the screen popping off due to the battery swelling. i brought it up to the supervisor and she said don't worry - we'll replace it free of charge. I should be mailing it back Monday and hope to have a new one by the end of the week. I did ask if it will be a series 0 or something different. the rep said it will be the exact same model. a bump in processor would be nice but for how i use it - the same would be just as good. shinny too. I feel lost without my watch on.