Replacements found here on amazon.com  replacements cost $33.75 w/shipping as of 04/14/13

These newer batteries also have 25% more capacity. 

How to replace the battery pack:

1. Remove the 4 screw that hold that top half case

2. Now that you can see the battery pack, remove the 3 screws that hold it in on the underside of the case.

3. disconnect the 3 plugs that are above the battery pack and power supply board.

4. Remove the 3 screws that hold on the power supply board

5. Move the PS board up and over the transformer.

6. Remove the QDs from the batteries.

7. Remove the screw on the back of the case that holds the battery pack and the 4 screws that hold on the back.

8. Lift the back of the case up and slide battery pack out.

9. Replace with new batteries and reassemble.