Is there a problem wearing an automatic watch over a two day yom tov? If left unworn the watch stops running even on full charge after 36 hours. Thank you.
According to most poskim it is permitted, and that is the minhag. On a two-day Yom Tov, although it is permitted, as you say, since it will not last that long on its own it is a nice chumra not to wear it.
Chelkas Yackov 1-75, Shalei Tzion O:CH pg. 103, Tzitz Eliezer 9-20, Mishne Halachos 8-59, Shmiras Shabbos Khilchoso 28-ftnt 57 in the name of R’ S. Z. Auerbach zt”l, Ashrei Hoish O:CH 2 Chap.33-3, Divre Chachomim O:CH 295 in the name of R Schienberg, R’ Yitzchok Berkowitz shlit”a.