Ahhhh thank you brian i didnt know that. My 300zx is a 91 so im not entirely up to date on things like that, hell its OBD1 i forget how useful sensors and readers can be sometimes haha
I hate how computerised cars are now. The 90s was the peak for me.
Battery has no sway on your cats. They either pass or they dont. Im not familiar with CA emisions testing but the battery is just that. Whether your exhaust system is up to snuff wont be affected
It's not about the battery affecting the cat, it's about the ECU(s) losing the learned/calibrated data that isn't hardcoded in. Cars 2000 and newer no longer get a sniff test, they only check using the OBD system. Modern cats have 2-4 sensors and if the ECU isn't recalibrated, you can fail because the readings are "wrong". Once the newly calibrated data is stored in the ECU RAM, you're fine. This is also a good argument for why you need to buy OEM parts and sensors. If you buy a new cat or o2 sensor at AutoZone, the ECU may come back with a fault. The only way to fix it is to take the car in so the ECU can be calibrated manually to the replaced parts.
Brian, I am sure you already know this, but for the others, what you are describing is called the "I/M readiness" test.
I don't use additives and almost exclusively go to Costco for gas.