Arduino Resets Upon Bluetooth Communication

I've been having some trouble with my bluetooth project. When I have my arduino uno powered via usb i can send value for a servo to turn to over bluetooth no problem. However, when I detach the usb and connect a nine volt battery to the power jack the Arduino resets every time I send data over bluetooth (using the serial monitor). Does anyone know how to fix this?

Sounds like you have a current sourcing issue.

Fresher battery?
6 x AA?

I'm using a nine volt battery which is fairly fresh but I'll get a new one and swap it out. Thanks!

I'm using a nine volt battery

Not a good idea - no matter how fresh.