"John Kimmel" wrote

Here is a picture of the insides of a tiny tach. The gray stuff is soft
potting compound similar to BMS5-95. The battery was a common 3v Lithim
Ion button cell welded to the tabs before potting. If I ever find another
tiny tach that needs a new battery, I will cut a hole right over the
battery with a rotabroach or a mill instead of splitting the case. You
can't open the case without breaking it

http://tinyurl.com/tinytach

My tactic for splitting plastic cases is to use a dremmel tool with a thin
cut-off wheel, and cut right on the seam. Don't bother trying to pry it
apart, since they always crack like you have observed. When putting it back
together, I use JB Weld on the seam and quickly put electrical tape over the
seam. This holds the case together while the JB sets up and the tape will
later peel off, leaving a nice slick seam of JB. On a black case is
difficult to see that it has been taken apart, since the JB Weld becomes a
smooth surface that matches the plastic case amazingly well.

I have used this method to replace cells in power tool battery packs, and
the repair holds up to the extreme abuse they are subjected to.
--
Jim in NC