I don't want one with batteries to change. Builder put mine 20' up a wall. We don't want to have to change batteries on it.
How many did he install? There should be one in the hallway just outside each bedroom and they should be wired to all go off at the same time. Call your idiot builder back and tell him to put the alarm where it can be reached with perhaps a 6' ladder.
Re your question, they all have battery back up in case the power goes off.
Our master bedroom is on the first floor of a 2-story house. Our foyer is 2-story, and the master is off the "far" (from front door) end of foyer. There's a small "foyer" from the main one where you gain entrance to the bedroom, powder room, and hall closet. The ceiling of this little space has the air exchange, and so he couldn't put the smoke detector there. Step right outside that space--back into the main foyer--and you're in the 2-story part, so 20' up over that space's entrance is where he put it.
There's NO way we will be able to service that thing. It was ridiculous to think that we could.
I am at a complete loss to understand why there is only one smoke alarm in what I presume is your very tiny house! And then it is inaccessable. Have I got everything correctly.
This is not the only smoke alarm; it's just the only smoke alarm that I have an issue with because it's inaccessible due to its height on the 20' wall. This is the smoke alarm "outside" the first floor master bedroom. There are 3 bedrooms and bonus room upstairs covered by alarms, and there's an alarm in the basement outside the basement bedroom.
If you are still in touch with your builder, I would inquire of him how he expects the offending smoke alarm to be serviced.