Longer lasting means less degradation on battery from charging wear and tear. If a battery is good for 500 cycles then it would last for about 1 year 4 four months at 1 charge per day. At 1 charge every two days it'll last about 2 years 8 months. 2 day battery life is so 2012 though. We should be at 1 business week battery life by now.
Battery technology is actually not progressing that much, though. Most of the gains we get are from A)Bigger Batteries B) More efficient chips and C) More efficient software