A:AnswerAs long as they are not associated with another person’s Apple ID, they should register easily with yours. If needed, you can reset the device (not wipe the ID) by removing and reinstalling the battery 5 times.
A:AnswerYes. There is a battery inside each one. They last for a year or two and are easily replaceable when they die. Your phone will alert to you their dying battery.
A:AnswerNo, but you can log into any device that can access the internet and log in to iCloud.com or I use my Apple Watch. I ask Siri to find my iPhone. If it’s within range it will start playing a loud noise even if it’s on silent
A:AnswerYes, you can replace the batteries and these batteries don’t need to come from Apple. You just twist off the back of the tag, remove, replace and re-twist. I am not a handy gal, but this was not a problem for me.