I just make sure my phone is fully charged before any outing. I had a nice portable charging device for a long time and never ever used it. Tested it one day and it was a goner.
If visiting away from home, I'll just take my outlet charging cord. Even when in the hospital overnight, I had a plug right by my bed where I could have plugged in my charging cable. But, it wasn't needed. I was only making calls, which isn't a battery drainer.