I have a couple of dozen devices. I'm changing batteries all the time. I can't remember when I changed batteries last. This is information that's useful to know – to monitor the quality of batteries, or usage of the devices.
There's no way to do this with the current app. You change dead batteries, and if the time and date are recorded, there's no log for you to see.
If there was a log, you could see when batteries needed to be changed based on history, and change them proactively.
Again, this is an easy improvement to system usability. The data is already available (when a battery is depleted you are sent a message, when it's replaced with a full one the warning is extinguished). Its recording needs to be made available to users.
Add a Battery Change Log field in the app for each device.