Not sure why you quoted my post. I never said I let it die. In fact I usually charger it around the 20-30% range. Anf you are wrong about the 50%. Just as long as you dont let it die all the time is fine. Doesnt matter what percentage you start to charge. Actually the best thing to do for the battery would to be turn the phone off if you arent using it. But obviously it would be silly to turn your phone on and off all day.
I thought u said in yr Post #3 "Meaning that I go a night without charging it".
The percentage at which you recharge is critical in determining the overall longevity of yr battery.
Battery university says that it's best to keep a lithium ion or lithium polymer charged up at all times.
Meaning that if u can, recharge it even after the slightest fall.
A battery discharged 100%, and then recharged, will last only 300-500 cycles.
A battery discharged 50% before being recharged will last 1200-1500 cycles!
Meanwhile a battery discharged only 10% before being recharged, will last 3,750-4,700 cycles!!!
The more you keep it up, the more you will prolong the life of yr lion or lipo:
How to Prolong Lithium-based Batteries - Battery University
Refer to their Table 2.
Thus, for a 1520, for practical purposes, best recharge nightly.
Allowing yr battery's capacity to fall to 20-30% before recharging will shorten/reduce the overall lifespan of your battery...