comments:
leexgx posted on r/airtags41w
Probably could get something that is CR2032 something like https://a.co/d/0h3HNnKJ so you can wire it up to an ER18505 battery (approx 10 year battery, its not rechargeable but has extremelylow self discharge l, these are used in smoke detectors) Don't worry about the voltage as airtags and smarttag2 can handed upto 5v