Battery life so far has been fantastic. I've practically been living on this thing for the last week because I really want to test it well while the window to return it is still open. I'm getting about 9 hours of screen on time with it so far from a full charge. Email, web browsing, social media, youtube, mild gaming, light Netflix, and a little bit of simple photo/video editing. And this is all while the tablet is connected to the keyboard, so it's providing constant power to that as well, but apparently not enough to cause any significant battery drain.
I'm spoiled rotten from the fast charging capabilities on my Note phone....I got from 15% to 100% in maybe 90 min. It takes roughly 3 hours to gain a full charge on the Tab S4, but I need to remember that I'm dealing with a much bigger battery.
I'll also throw my 2 cents out there regarding the keyboard. I saw a lot of critical reviews of the keyboard before buying, but so far I've been largely impressed by it. It's definitely a bit on the cramped side, but I'm adjusting quickly. I'm a decent size guy....5'11" with large-ish hands and I don't have much issue navigating the keyboard. Anyone with smaller hands should find it comfortable to use right from the start. I do find that when I'm trying to type out a couple of numbers or special characters, I sometimes might incidentally hit the onscreen home or back button with a stray finger. This could easily be rectified by hiding that bar completely, but I'm learning to adjust the way I hold my fingers. (Side note: I'm generally not this wordy in these forums, but this is giving me great practice with the keyboard. lol)
There's a Language button on the keyboard that for some reason I manage to keep catching with my right thumb whenever I go for the space bar. It's pretty pointless and I wish there was a way to do some key remapping on this thing because I would gladly disable that button completely along with the button that brings up an on screen keyboard. Not sure why I would need an on screen keyboard with I'm using the physical keyboard, but Sammy decided to put it there anyay. There's also an app drawer button just like the one found on Chromebooks. When you're on the Android side, that button wakes up the Google Assistant, but when you're on the DeX side it actually opens the app drawer. This is another one I'd like to remap if it were available. I can wake up the assistant with voice commands when I'm on the Android side so I'm not sure why I need a key to wake it up just so I can then give it verbal commands. Would much rather be able to remap it to open the app drawer in Android mode as well. Maybe someday...
Overall it's definitely not the worst mobile keyboard I've ever used. I've tried maybe a half dozen or so over the last 10 years and I'd actually say this one is the nicest so far. $150 is a steep price to pay though. Luckily I noticed Amazon was selling them yesterday for $102, so I went back to Best Buy and they price matched it and gave me a $48 credit back on my acct.