<font color='#008080'>Battery replacement is fairly straightforward. Just make sure that if you want to reuse the o-ring you don't nick it during dissassembly. The battery is a 3V lithium CR2450.
I replaced mine at the start of this season and reused the old o-ring after checking it for damage and applying some silicon grease to it.
I got a kit (battery and o-ring) for £5-95 from Deep Blue Diving:
http://www.deepbluedive.com/products/products.asp?catid=22&manid=2
Best
Anke