lidnariq wrote:The cabinets always have mechanical coin counters as well, so it's credible that this is intended only for tracking coins since the last power outage.
Agreed. The coin distribution count screens do not alone confirm battery use.
However, we have established that all the VS PCBs are nearly identical. They all have battery holders and when batteries are installed, the memory in range $6000--$67FF (and mirrors) is made non-volatile. Nonetheless, we only care about which games actually take advantage of that fact.
As a test, in my emulator, I persisted the data in that memory range on shutdown and restored it on start up. The coin distribution screens in VS. Balloon Fight and VS. Ice Climber (Dual) maintained their values. So, if the battery works like we expect it to, then those 2 games appear to be taking advantage of it.
Furthermore, the VS. Wrecking Crew high score table is retained.
But the VS. Raid on Bungeling Bay high score table is not! I can see the table in a hex dump of the shared memory region, but it's not maintained between bounces. It'll check if there's another copy in CPU RAM.
As for VS. Mahjong, I can't tell because I can't read Japanese.
My conclusion thus far is that VS. Balloon Fight, VS. Baseball, VS. Ice Climber (Dual), VS. Tennis and VS. Wrecking Crew all use battery-backed non-volatile RAM. And only VS. Raid on Bungeling Bay and VS. Mahjong (probably) do not.