PSP Power Saver turns off the UMD driver when you are not using it. This should save you about 5% of your battery power.
Changes:
-Fixed compatability issue with the 5.03 Gen-A firmware, some funky shutoffs were going on
-Cleaned the source up (NOW CLOSED SOURCE, due to a certain someone that I thought I trusted, modifying it and causing a rukus)
-Added vsh support
Source
This article is over 2 years old — the linked page may have changed, moved, or been taken over since then.