Yes, unlocking your bootloader will void your warranty. However, you can usually re-lock your bootloader if you need to return your device for warranty repairs.
In the rooting community, modules like Xtreme Battery Saver (XtremeBS) or 3Minit Battery Mod are distributed as .zip files to modify power profiles or battery icons. 3. Physical Battery Lock Fixes If you are referring to a physical lock that is stuck: Unlock Battery.zip