Oh hey you’re here! I love this series. Warrier was my favorite so far but they’ve all been excellent!
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.
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.