Dell Inspiron N5110 - Speakers don't work when power is unplugged

Hi.  When I unplug my power adapter to take my laptop somewhere, my speakers don't work anymore.  

To get it to temporary work for a video, I have to go

Sound > Speakers/Headphones > Advanced > Test ... and I will have sound.

When I watch something on VLC player or online, I have to do that for my sound to work.  Sometimes when I stream my shows on google chrome, my sound don't work at all.  I would have to plug my power adapter in for it to work, and do that Sound > Speakers/Headphones, ect. thing again.

Is there a way to fix this????