While it's been documented why this is, but you didn't ask that, I'll stick to what I do.

A few things actually.

1. I put my phone into airplane mode a lot.
2. I follow the ABC rule (Always Be Charging) since I don't want to buy a new battery in year 2. This rule, batteries is well discussed.
3. If I do want cell service I'll disable bluetooth, WiFi, GPS and data use.