Mediaserver using excessive CPU time and battery
Killing all running apps didn't solve the problem, nor did disabling the automatic sync for Google account items like videos/photos (which I heard suggested for a similar battery issue).

What did work was simply rebooting the device by holding the power button and picking shut down. After rebooting Mediaserver no longer appears to use much of my battery in the usage chart and my charge lasts like it always did. So if you get the same issue, just reboot.