Ok, assuming you unplugged the power before removing the battery you've done a proper reset now.
Ideally you should've tested the RAM after the reset but before the reset any combination of slot and stick you tried still gave you the same A2 error, right?
Again, ideally you'd want to do this after the reset and with no hard drives connected, but let's assume you did it correctly if you're not willing to do it again.
The options left are:
1. CPU is fucked and the mobo isn't giving you the right error code for some reason.
2. All RAM sticks and/or all slots are dead and the mobo isn't giving you the right error code.
Both of these do seem unlikely because the error codes seemed to work for everything else. Of course this might change after the reset, which is why you should've done that first (that's why ASRock tells you to do exactly that in the error code FAQ).
Anyway last option:
3. Your mobo is fucked.
If you've got access to another mobo with DDR4 you can check the RAM. If you can somehow get access to another Z370 mobo you could even test CPU.
My money is on the mobo though.
knsumey'know, i've always wondered why setsul always seems a bit annoyed when he answers tech questions
now i know
Tech support in written form is always challenging because most of those problems only exist because people failed to read written instructions so trying to solve them by writing instructions for them might not have the best success rate.
At this point I always seem annoyed even if I'm not because it leads to more people following the instructions to the letter, which leads to less annyoance for me.