If you're worried about the battery update, here's how you opt out of system updates

Maybe I'm just paranoid, but there's precedent for manufacturers intentionally hurting the performance of their old phones with software "updates". Never assume a company is doing something out of the good of its heart, ever - that's my motto.

Here's how to disable system updates:

1. enable developer settings by tapping the build number in About Phone
2. go to Settings->System->Developer options
3. Find "Automatic system updates" and turn it off
4. Done! :)