Might take another look at these - given the price, it's not a huge gamble to try it out for a few weeks.
They have no idea where they are or what their airtag/BLE neighbors, if present, are doing. They don't grok GNSS or wifi. There's nothing for them to triangulate or trilaterate or tri-anything when they're just sitting there.
So yes: They are indeed pretty tidy about energy consumption. They accomplish this in large part by being very simple in normal operation and leaving the heavier lifting to the world of iPhones with relatively enormous batteries that get recharged ~every day.