I know this topic is a little old, but I think someone else might find this information interesting:
software.intel.com/en-us/blogs/2012/03/30/battery-life-on-android-what-can-you-do
ii. Mediaserver. This system process is tricky when it comes to battery. What happens is that whenever you access any sort of media on your external SD card (playing music, gallery, what have you), this process kicks off. Luckily though (but hard to catch), sometimes, this process uses more process time than it should due to corrupted contents on your external SD card. In order to catch this culprit: try clearing your battery stats (for example, restarting your device or coming off AC power), playing some music and/or checking out pictures on your SD card for a few hours. Then, check your processes. If Mediaserver is high up there in usage, you may want to consider cleaning up your SD card. Naturally, we would expect that the process is higher when media contents are in use. I can’t give you a specific guideline such as, "something is up if Mediaserver consumes over 25% battery." This is another example of where you should look up other user stats for system processes based on your specific phone and OS version. If you think your SD card may be corrupted, backup your data, format the device, and slowly, add back files and repeating your media tests. Finding a corrupted file isn’t a guarantee, but this doesn’t hurt if you suspect data corruption.
