Quoted from phishrace:
Aren't you a little curious on the voltage reading? It looks spectacular for being 35 years old.
Next time I am at the machine, will check the voltage on this old battery.
Thanks everyone for the great tips on what to use.
I had been using memory caps as my go to replacement. It should work great in this SYS 80 board. However, I just recently learned (on pinside) that memory caps aren't a great option for the WPC games due to the clock draining the cap voltage down too quick. NVRAM is also not a good option for WPC due to loosing the midnight madness on certain games. So what's everyone been doing on WPC these days?
The best option I can think of is a remote battery pack on long wires lowered down in the cab, placed in a ziplock bag for good measure. Perhaps down by the coin door. I don't like keeping the battery pack in the head, due to the proximity to boards. Even if you get it away from the MPU, if it's still in the head it's going to be nearby another board.