I'm a Search and Rescue member on call 24/7, so I need notifications at a loud volume at night. I fixed this in my Verizon G3 with the following process (which may void your warranty...):
1. I rooted my device using IORoot. Other models may be able to use the simpler towelroot.
2. I installed SuperSU to verify and manage root access
3. I installed Root Explorer (File Manager) to rename files, and install new ones.
4. I found a silent OGG sound file on the web
5. I made two "silent" copies -- A) FullBattery.ogg, and b) cam_snap_0.ogg
FullBattery.ogg replaces the tone with silence. cam_snap_0.ogg replaces the loud Camera App shutter.
6. I used Root Explorer to navigate to /system/media/audio/UI
7. I renamed the existing system sound files FullBatteryXX.oggbak, and cam_snap_0XX.oggbak
8. I copied my new "silent" files to the same folder.
9. I disabled root access in SuperSU.
Result: Silent shutter, and no battery full beep! I can't believe these aren't regular options. I can't imagine anyone has any desire to hear the Battery Full beep, esp in the middle of the night!
The process wasn't super difficult, but read the various rooting tutorials carefully before trying. It worked for me the first time...