While I was working in my laptop, I found that there was volume, battery icon missing from panel, I don’t know how. After some research I found a easy solution for this.

Solution:

Step 1. Right-Click on the panel
Step 2. Add to panel
Step 3. Select Indicator Applet then click Add
Step 4. Click Close

Indicator Applet Looks like :

This should solve your problem. If you can’t see the changes try restarting the panel. Open terminal and Use the following commands.

asee@asee-hp:~$ pkill gnome-panel

The above command will refresh your panel, and now you should be able to see the volume, battery icon in panel.
Leave comments, if you find any difficulty in doing this.