mares bottom timer

Question
Hello, I have a Mares bottom timer thats fairly old.The only numbers on it is 09.91 and the face has green,yellow and red color bands across it.There is three metal contacts on the front 9,12,3 o'clock position. I need to change the battery and it appears to be sealed. Can you help me out? Thanks Bob

Answer
I remember those.

You'll definitely want to do one of the following:

1.  (recommended, and per manufacturer) return to an authorized repair shop.  (some don't fix older computers, so this may or may not work out)
2.  google how to open it (you may have already).  I have a feeling there is a trick to opening it, and you may have to be careful of it being filled with oil too, so you don't want to botch it.

Hope that helps... not much info but I don't own one of those and I've not opened them.  I have a couple old Uwatecs in the same condition that I need to fix one of these days...

dive safely,
James