Hey,
it's not that easy I'm afraid. The battery type you want is a Li-ion called "18650" - but it is soldered into the DAC. It is attached to a small circuit board (aka. PCB) which regulates the charge. I can point you to this replacement
http://www.batteryjunction.com/2600pcb-18650.htmlwhich hopefully should fit in your unit. You'll need soldering skills to install it however.
This guide will help you disassemble the DAC:
http://www.cool4u2view.com/Neuros_files/Page721.html-G