I dont think there is a definitive answer, but as its new id suspect You have updated the device and played with settings which will disrupt your battery to a degree. I'd first of all try clearing your device cache partition, follow this youtube vid to show you how.
https://youtu.be/3mvRvEsAPpEI'm not sure if yours is lte or bt version but if you are in a weak signal area and have lte always connected it can drain the battery if your watch is struggling to connect to lte, so id only enable this is you need it (set it to auto rather than always on). I'd make sure that wifi isn't connected unless absolutely needed as you can use Bluetooth or lte instead. Mine seemed to die quickly at first but it did seem to calm down after a few days. Hope this helps
