If you expect good battery life, don't install the beta.
Simple as that.
A beta is for people to check it out, and report feedback. It's not for day to day use; it's not for your "main phone". Although, I suspect, many here use it on their main phone, and so do I. But at least I have enough sense to be aware of the fact that there may be many crashes etc.
Now for something completely different: I sent a bug report to Apple complaining about the fact that the new Messages app doesn't display time stamps; it shows only one time stamp per day, but not timestamps on individual messages. Now they're asking me if it happens on beta 3 too - this is weird because to me this looks totally intentional, and I see it on all messages, there's no timestamps anywhere. Does anyone else see this?
E.g. in messages, see if you can find a conversation where one message was sent, say, an hour after another. Does the second message have a time stamp on it? It used to, and I absolutely need to know when messages have arrived....
See the attached. Note how the last message in this thread is a bit offset from the others. That one was sent much later, like hours later. But no timestamps. Stupid.