I'm not sure how many people are on recent versions. There was a thread about someone here updating to Oreo and being OK, but it's the only data point I've seen. Many, including the vast majority of Shield owners it would seem looking around here and the DJI forum, aren't willing to update! May not get much data regarding recent Android versions.
I plug my Shield into the lower USB port of the controller. I have 2 batteries. Flying through both of them, combined with some dorking around checking my RTH and camera settings first, looking at maps between batteries, and so on and I've got my tablet plugged in for almost an hour. At least 45 minutes. I am pretty consistently at about 65% power left on the RC after all this. So while the tablet does drain the RC batteries, for my uses that's fine. I know if I was trying to perform an actual film shoot and had to be up for a few hours straight I'd be frustrated and running out of juice. But for a hobby I'm good.
Couple notes:
* The RC shows a strange battery % while the tablet is plugged in, I have learned not to trust it. It shows the 65% or so after I've unplugged the tablet and started packing up. It shows this same amount when I get home and put it on the charger. Not sure why goofy %'s show up w/ the tablet plugged in, maybe it's some wort of weighted average? I haven't looked into it.
* It does appear you can use the USB port on the side with a battery pack. The issue with the lower USB port not working simultaneously is limited to the iphones / ipads. DJI is doing something interesting to keep them from charging from the controller, and whatever that is keeps both ports from working at the same time. Android can use both. Well, mine can (and my iphone definitely cannot). I've tested that this works, but have not bothered to see how well it works (how much power is restored / not lost to start with / run through the RC from the battery pack to the tablet) since I realized I don't actually need it.