This is an excellent post, one others should follow. Please allow me to make one minor change to this process. Instead of starting the 2nd power down charge at 20%, wait till you get the "Low Battery" warning at 15%, then follow your original plan. The low battery flag is set at 15%, so if you don't discharge to that level, the charging and monitoring circuitry never actually gets a true representation of the full range of the battery. This could result in the meter showing more power available than it actually has, and that could lead to boot loops, power cycling, or possibly to an unresponsive phone if it were to shut down on its own. Otherwise, ROCK ON!
Originally Posted by BillyT
The following is an excerpt from BatteryUniversity.com. Note, they show the low battery flag set at 10%, but for the RAZR and most other phones it's actually 15%. Otherwise the information is accurate.
The fuel gauge has the inherent drawback that it needs periodic calibration, also known as capacity re-learning. This is unfortunate, but is required to correct the tracking error that develops between the chemical and digital battery over many charge and discharge cycles.
Calibration could be omitted if the battery received a full charge followed by a full discharge at a constant current. This way, the battery would reset with each full cycle and the tracking error would be kept at less than one percent per cycle. In real life, however, a battery may be discharged for a few minutes with a load signature that is difficult to capture, then is partially recharged and stored with varying levels of self-discharge depending on temperature. These anomalies contribute to an unavoidable error. The true capacity of the battery begins to deviate from the fuel gauge readout and the battery needs to re-learn. Battery engineers say jokingly that “Li-ion got rid of memory and SMBus adds digital memory.
Calibration occurs naturally by occasionally running the equipment down until the battery is fully depleted and “Low Battery” appears. The full discharge sets the discharge flag,
and the subsequent recharge sets the charge flag.
By establishing these two markers, the battery can calculate the state-of-charge by knowing the distance between the flags. Figure 1 illustrates the full-discharge
and full-charge flags.
| Figure 1: Full-discharge and full-charge flags
Calibration occurs by applying a full charge, discharge and charge. This is done in the equipment or with a battery analyzer as part of battery maintenance.
Finally, it is recommended that you do this about once every 3 to 4 months with the MAXX, and once every 2-3 months with the RAZR (different battery capacities warrant less or more frequent trainings), or every 40 full charge/discharge cycles where a full cycle is the sum of 100% of capacity.
For example, using BillyT...he's going to have 100% of capacity at the end of his 2nd powered off charge. If he then uses the phone for 50% of the total charge capacity and charges from there to 100% again, he still needs to use another 50% of the next charge cycle and then charge back to 100% to have effectively used a 100% charge cycle (50% + 50% = 100%). He can also use 80% of the charge, leaving 20%, charge fully and then once he's used the additional 20%, he would have reached the 100% capacity cycle (80% + 20% = 100%). This method of keeping track is difficult - especially over 40 charge cycles, so I say try sticking with a schedule as mentioned earlier.