After replacing the battery in the AirTag attached to my keys I have continued to get low battery alert after alert.
Doing some research it seems manufacturers often apply a coating to button cell batteries to prevent children from trying to eat them and this coating can prevent the power circuit from completing.
The solution is to either buy batteries without the coating or to remove a small amount where the battery contacts with the AirTag. You can use an alcohol swab for this or even a pencil eraser should be enough to wear down the coating.
Remember the coating is there for a reason so be sure to keep safety in mind when leaving AirTags anywhere children may be able to get to them. While they’re designed to be difficult for a child to open them it’s not unheard of.