Just dug out my old Viper030 board, and am looking at it now. Its just a standard CR2032 battery & it's not soldered, just a spring clip holding it in place, just replace the battery with a new one and see if it works, theres a pic of it somewhere in my profile section.
Hmm... strange but the one I have looks different to the one in your pic, dunno if mines is an older model...
