My battery has fallen below the 80% threshold for battery health, so my new thing is setting a stopwatch when I take it off a charger, to see how long it lasts, and in many cases, placing it in airplane mode at least.
And bought an external MagSafe battery. How long does 5500 mwh power a phone?
Have you had a battery replaced at the Apple Store? How long might you go without your phone? Any data loss beyond it possibly being out of commission as a notification comes through?