Who I have the same questioned this topic

I have an older Droid Maxx 2 that has randomly shut downd for the last month or so.  It will say "battery low" and shut down even when the phone show 80%. I can power it back on and it will stay on for a few minutes and then shut down again. I have to plug it in and charge to 100% for it to work again.  I have not removed or added any new apps. I've cleared the cache. I don't want to factory reset and lose everything.  What's up?