Power reserve on Apple Watch won’t turn off

Power Reserve should end once your Watch is recharged to 80%. You can exit almost anytime by pressing and holding the Side Button (long button, not the round Digital Crown). But if you can press and hold the Digital Crown to activate Siri, you shouldn't be in Power Reserve.

Hello,

If the battery has been drained to a certain level, power reserve can only be turned off my charging the watch.

Hope that this helps!