I've never done a CPS1 battery but it looks like you have to come from the underside to do it.
Yea, It looks pretty basic. Just 2 Points that need to be Soldered but do the same rules apply as the CPS2.
Would also like a good place were I could buy the batteries.
How many do you need? I'm almost positive I have 4-5 left from when I ordered a pile last year and had these left over.
but now that you can rewrite keys its kinda a moot point.
I swear by these. You can find them for ~$7 if you shop around.
I always buy mine from RS.com, used them for years without a hitch.