This week I was travelling by train and my Kindle-browser didn't work.
I restarted my Kindle (home-menu-settings-menu-restart) and the browser was fine after that.
What I didn't realize at that moment that the restart
emptied the 'search-indexes' and the Kindle started re-indexing all my books (1182).
The day after I noticed my
battery was almost empty and as I had it charged two days before my travel, I investigated why and discovered the re-indexing.
It took more than 24 hours to complete it. I checked on my PC (via USB: Kindle-system-search indexes)and all indexing in the folder was from today and yesterday and
nothing else.
Most of the times when something is wrong with the Kindle, I just reboot and usually that fixes it. Weird.