What does Kindle Fire Optimizing Storage and applications actually mean?

Every time I boot my Kindle fire 10 7th gen, it does this. Sometimes displaying "Optimizing Storage and applications" with progress bar for up to 10 minutes. The flippin thing runs out of battery while unattended often so this issue keeps arising. Does anyone know what its actually doing? Common usage is: View a web page or two. Watch a YouTube video. Rarely do I Install new apps or download data. There isn't much new on the drive to optimize between reboots! If there are some logs to review, Id love to know which ones and I could post snippets here.