We have two Shelly Button 1 devices: Physical buttons that when pressed, connect to the Wifi network and do HTTP requests. I configured one to switch lights in the living room on and off.
The bottom case of the button fell of; when inspecting that I saw that the lithium ion battery was too thick to fit into the case:
Shelly support wrote in German:
Eventuell liegt ein Defekt des Li-Ionen Akku vor.
Wir bieten diesen Akku nicht als Ersatzteil an,
laut Spezifikation handelt es sich um einen Li-Ionen Akku 3,7V, 400 mAh.
and the English translation:
The li-ion battery may have a defect. We do not provide replacements for this battery, according to the specification it is a Li-Ion battery 3.7V, 400 mAh.
According to a Thread on shelly-forum.com there are replacement batteries on Aliexpress with the name "652530" - but switched cables.