Ipad pro 10.5 - battery drain after update to IpadOS 13.3.1

I had this problem for a while. I took it in to Apple Store and they recognize it's a problem. They tested the battery and its health was at 85% and no need to replace. They performed DFU reset and still same issues. Suggested replacing the battery for $109 (out of warranty cost) and still $!@#! issues. Third time I took it back to Apple Store, some half-trained rep said it was normal and my expectation of 2-4% drain over night is just an expectation and not guaranteed or stated by Apple on iPads. What a bunch of BS!!! Finally, I've realized that it was WiFi that was the culprit. I put it in Airplane mode over night and no battery drain of significance. It is annoying that I have to disable WiFi each time I put it in extended standby (e.g. overnight) but at least I have a workaround. I am not sure what Apple did in their OS updates but they messed up. And I am out $109 and Apple store won't refund it.

Not a fix, but for information...

Objective measurements across a number of iPad Pro 10.5 devices (with iOS 13.3 or 13.3.1 installed) indicate that atypical battery consumption to be about 13% capacity per hour of moderately intensive use / web browsing; typical overnight drain, with email set to fetch every 15 min, is in the region of 2-4%. Typical battery life, for continuous use from a full charge, is around 7.5 hours maximum.

Your indicated battery utilisation is much higher than expected. It might be worth attempting a simple “restore” using a PC/Mac (ensuring that you have a current iCloud/iTunes backup before starting). Other than the time it takes, the restore process is benign to your data (assuming that your restore from the backup) but the process does completely reinstall iPadOS. This may help, but if it doesn’t improve matters, it certainly won’t make it any worse.

As already mentioned by MitchelPM, anecdotal evidence suggests that - contrary to logic and normal expectation - several consecutive forced-restarts immediately following an iPadOS update, frequently resolve various persistent problems.

I hope this is helpful to you.

Have you tried a simple hard reset of your iPad by holding down both the Home and sleep/wake buttons simultaneously until your iPad goes to black and restarts with Apple logo, then release the buttons, AFTER you did the OS upgrade?