I've never understood the need to have a phone last weeks on a single charge.
For me, usually when I'm having a really long day, it corresponds with using my phone a lot. Like a day stuck in the emergency room for a family member. I'd already had a full day's use of the phone, then spent the next 8 hours having to call family and friends about what was going on. My phone had already gotten normal use that day, so it was at about 30% when I left for the hospital. The brief charge it got on the way took it to about 40%, but with all the calls, texts, etc. by the time we were done the phone had been dead for 3 hours. I've taken to stashing a USB battery charger in the car. It stays plugged in, and can throw a full charge into my phone when needed.