How can I replace the back glass of my iPhone, and will my phone still be waterproof after replacement

It was never waterproof, just water resistant. And even AppleCare just provided a slightly lower-cost replacement for water than basic warranty.

Take it in for an estimate for the cover AFTER getting a backup. There is a 50-50 chance they will just replace the unit completely.

sberman wrote:

In addition to steve359’s response, with which I agree, you should never deplete your iPhone battery as far as shown in your screenshot.

To be fair, damage that externally shows as back-panel broken could cascade rapidly ... logic board gives false readings or battery cracked or ...

Your point is still correct, though. Running it that dead shortens the life of the battery. Battery-sticks run $20 these days (Target, WalMart, BestBuy, etc) and can prevent running that low even when away from ALL wall-plugs.

In addition to steve359’s response, with which I agree, you should never deplete your iPhone battery as far as shown in your screenshot.

OK.

I never alluded to the cause of the extremely low battery, only the result.