I was awakened in the middle of the night by the chirping of my Nest Protect smoke detector. I had not received any warnings in the Nest app that the batteries were low. The batteries are the Energizer lithium that came with the unit. Three of the batteries were too hot to touch. I removed the batteries from the detector and put them outside, and have stopped using the detector. This Protect is a second-generation unit that was manufactured on September 14, 2017. I have four other Nest Protect in my home and am concerned about them having the same issue. I bought these devices to protect my home against fire, not start fires.
Sorry for the late response, but I wanted to drop in here to help.
I understand that these issues can be concerning but I definitely wanted to stop by and see how I could help.
Just wanted to double check to see if you were still needing help on this? If so, what troubleshooting steps have you tried?
Please let me know.