This is the reason I don't like using a lithium button batteries for this application - just in case the original or even a better replacement diode fails.

An alternative backup method that works well is by installing 2 x 1.5 farad supercaps in parallel instead of a lithium battery. I think I got more than 2 months backup with this (on a system 6 game).

I think from memory the easiest way was to connect direct to one side of the blocking diode to allow the power to flow to the caps with a 100ohm resistor to regulate the current.

Also, if doing supercap conversion, best to have a Philips PCD5101 as they have the least current draw of all the 5101's.