Bluetooth Battery?

Hello everyone --

I have a simple bluetooth setup that works fine under USB power, but when I try switching over to batteries, it no longer works.

My setup is an Arduino Pro Mini and a Bluetooth Mate Silver.

I have a 4xAA battery pack wired to the RAW input of the Arduino.

Firing it up, everything makes a connection, but I only ever get -1 from the serial stream.

Am I missing something simple here?

Thanks in advance.