I just got off a chat, where I was trying to find out why it drains batteries so fast, I have 2 of them, the one upstairs works just fine, but evidently this one can only take the energizer ultimate lithium batteries! Really? It's worked fine for over a year, now all of a sudden it's draining batteries, but yall want me to buy a specific one, which I'm sure you own, because that's the problem?! Yet it's not a problem with the other one right???? Yall are crooks. I'll throw away every nest device I have. This is bs. I'll never buy another nest anything.
I have 2 Protects and I don't work for Nest but do volunteer to help here in the Community.
Just had one battery run low and replaced it with the required Energizer Lithium battery. It is required because Nest tested that battery brand with the Protect. I've seen so many posts from users that have trouble with other brand batteries with the Protect.
You can also turn off the path light option. That will make your battery last longer.
They do have to be lithium but also there is a known issue reported among users of this, and the fix was only hardware replacement. (if nest fails to cover warranty for the issue if it is in warranty, if you're in the US, file a report of fraud to the Federal Trade Commission at https://reportfraud.ftc.gov/ )