And it's called beta for a reason. I had some app installed and monitor the CPU usage. Sometimes the CPU can go up to 100% and stayed there. There are some threads not being release and using the resources. A simple reboot should do it. Thats what causing the battery drain and lags.

If you want to try beta, wait for Public beta 4 or 5. By then, most of the bugs should be ironed out already.

You'll see an initial battery drain in a few hours or day depending on the data on your phone as the OS is re-indexing stuff. Give it a few more days and do a battery calibration once.

I did a beta test on 11 never had a bad battery life on my 7+. When the official 11 came out, I did a fresh install and restore from iCloud. Then comes 11.0.1 OTA update and battery is the same.

Now testing iOS 11.1 PB1 and looks more stable than 11.0.1

run down the phone to 0% and charge back to 100%

I have no problem with both apps on 11.1 but FB did became unstable before an update. Now it doesn't crash anymore

Battery usage and system performance