How does your 12.9" Pro do when in standby though? I've found that over the last couple of OS releases, regardless of iPad model, standby drain has increased. Back in the old days an iPad could sit there in standby for a day or two and not even drain 1%. That is definitely NOT the case anymore. I know things have changed a lot since then and these devices are doing a lot more in the background than they used to, but sometimes the standby drain seems excessive to me. If it's an app I'm using regularly that's causing it, I don't know what it is, because nothing shows up in the battery report. The only thing I ever see is Siri, and that's not even every hour. Only solution I've ever found is turning off wifi when the iPad wasn't in use, which tells me it might be something with iCloud sync.