It is easier than taking to the dive store.
1. The battery is from Radio Shack, CR2430, cost $3.45.
2. Next step take a piece of wood or MDF, a nice hand size, mark 3 points in a triangle 44.6mm (1.75") apart, use a pair of dividers for example. Get 3 allen head screws M4.0, They have a 7mm diameter head, (if you use different size adjust the centre distance by the difference in diameter), drill three 1/8" holes at the points of the triangle and screw in the screws with a hexagon hole for the wrench. This tool removes the bezel on the face of the computer using the little scoops out of the side of it.
3. Remove the screwed bezel.
4. CAREFULLY remove the glass face, there is a small slot at the side to help you.
5. EVEN MORE CAREFULLY remove the small rubber O ring seal and inspect for damage/cracks.
6. Remove the plastic face with all the graphics on it
7. CAREFULLY remove the computer module, take care there is a ribbon tape underneath that you do not disconnect
8. Remove the clip holding in the battery and remove, note the right way up
9. insert new battery
10. replace battery clip
11. most importantly, on the face of the computer there is a tiny reset button. use a needle or paperclip to press. I missed this and spent two days wondering why the 'ACW' was dsplayed permanently. I emailed Suunto and they said it must be defective and post it back to Finland!!!!
10. assembly is the reverse of the above. I used silicone grease on the rubber O ring to prevent nipping and ensure a good seal.
I tested it in the bath first, then did a second pressure test with a 130' (40m)dive!
Sounds complicated because I gave too much detail, but it is easy really. I am taking this time to write it all as I felt ripped off every time I got it replaced....
All I ask is a thank you if you use it...