You've done a beautiful job on the board Andrew.
I can see countless hours of your time and a lot of patience put into it to get it looking so good.

With the Lithium batteries ,  i've been installing them on the boards I repair for close to 7 years now.
I've found that the smaller type 20mm button cells like you've used don't seem to last too long when put on all WPC type cpu boards , or earlier Williams system 6 and 7  boards either for some reason.
On these type of boards I am now using a slightly larger  24mm lithium battery ,CR2450 which so far are working great and holding their charge.
The smaller 20mm type CR2032 do however work great on early Bally -35 mpu's and similar, I have one on my test bench that has been on the board around 7 years and is still reading over 3 volts!
The 20mm type also work great on Gottlieb system 1 , System 80 , Williams system 11 , Data east and Hankin mpu boards.

The previous repair to the board you've worked on here is only average from looking at it.
I'm fairly sure of the repairer your referring to , i've seen the Green texta before but then again it may be someone else
Either way , even though the repairwork is only average it really isn't good form to ever bag another repairers work no matter how bad it is  “even though you didn't name them the suggestion is still there”.
Just think that if the was done better in the first place and the board hadn't broken down , you wouldn't have gotten the job...so they've actually done you a favour....that's the way I always look at it.

Again , excellent job on the board!