A CPS-1 is made of three boards. The CPS-B chip on your B board changes between games. On later boards, the CPS-B chip remains the same but it has a battery to store parameters, making it different.
If a game attempts to use the CPS-B registers in unintended way, the screen goes to black and is locked like this.
The Z-80 battery you mention on CPS-1.5 is to store a private key that is used to de-crypt the Z-80 instructions.
And I won't even talk about the CPS-2 because they even encrypted the 68000 code and shuffled the GFXROM there.
For the original commenter, while you can’t exactly just flash new roms to play a new cps1 game, there is a darksoft kit that comes out very soon, and lets you run roms off an sd card. It replaces your original B board - so it’s sort of like a flash-cart for your base A motherboard. Check it out! It also runs cps1.5 games in qsound.
Spend an evening with http://arcadehacker.blogspot.com/?m=1 and marvel!
I'm the proud owner of both a real CPS PCB and a bootleg (but still vintage) PCB (they go in a arcade cab). If I'm not mistaken once you've got a CPS PCB, you can flash any CPS game you want on it.
As piracy was rampant with these, Capcom added a battery powering a Z80 on some CPS boards and if it was ever off, it'd erase the game. These Z80 are known as "Kabuki Z80". The issue is that... 25 to 30 years later, all these batteries started failing and these board would "suicide" themselves. So there are people out there who "desuicide" (it's the term employed) these boards.
They're a great piece of history and, well, of course Fabian Sanglard had to blog about it!
The Wikipedia page is a cool read too:
https://en.wikipedia.org/wiki/CP_System