Quote Originally Posted by galletta View Post
So I would not set an alarm to disconnect my phone at 80% or power it down at 20% without being sure of the top and bottom calibration limits. If they already have set 20% as what is reported as 0% and 80% as what is reported as 100%, then you'll actually be stopping the charging process at 64% (80% charged x 80% max) and powering down at 36% (100% minus 80% discharged x 80% discharged min). My math might not be correct but you get the idea.
We know that the 0% level is deliberately set high to prevent bad things that happen when true zero is hit. It's very likely that the max is slightly lower than true max - again, because Li-ion can be very, very badly affected by high heat at full charge.

However, your scheme above is supposedly the perfect way to run a Li-ion battery. Try to prevent full discharges, try to avoid full charges, and you will get maximum life from your battery, because the stress of large charge cycles leads to fewer charge cycles over the life of the battery pack. See How to Prolong Lithium-based Batteries - Battery University for a great article about these issues, including the depth of discharge affect on the lifespan of a battery pack.