Same here. Originally, it would get to 5% then shut down, but it's gotten progressively worse. The highest I've had it shut down at now is ~20%. My first guess was that it's an issue of battery degradation not being properly accounted for, but the news about (new) Pixels suffering from the same problem makes it seem like that's unlikely. Hopefully this issue is resolved via an update, because I'd feel somewhat guilty recommending the Pixel to people weary of Samsung phones only to have major issues arise.