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Common wisdom for lithium based rechargeable batteries is in order to extend battery life you should charge to about 80% and discharge to about 40%. I've read a couple of articles recently that suggest that this common wisdom isn't completely correct.
Some people replace phones frequently, so the battery lifetime wouldn't be a big deal for them. Others hold onto a phone until it fails, for them it does matter.
AccuBattery (an Android app) has these articles which they say is based on hard research, and they give their sources / references:
To summarise, in case the articles are removed in future:
- Not all the advice on the internet is based on facts / research
- Charging has two phases, constant current and constant voltage. The later starts somewhere around 80% of charge is more damaging for the battery
- For every 0.1V increase in battery end charge state the battery life is halved
- Charging in less than one hour damages the battery
- Charging to about 4.1V is best for the battery. Manufactures set their "100% charged" level at different voltages, which varies between 4.2V and 4.5V. My Pixel 4a hits 4.1V at about 79% charged. My wife's Samsung S22 hit it at about 85% charged.
- Discharge depth doesn't affect battery longevity. You can let your battery get as low as you like and it won't damage it. I personally prefer to keep it above 20% but that's for practical reasons rather than longevity.
The articles provide references:
- Asakura, K., Shimomura, M., & Shodai, T. (2003). Study of life evaluation methods for Li-ion batteries for backup applications. Journal of Power Sources, 119-121, 902-905. doi:10.1016/s0378-7753(03)00208-8
- Choi, S. S., & Lim, H. S. (2002). Factors that affect cycle-life and possible degradation mechanisms of a Li-ion cell based on LiCoO2. Journal of Power Sources, 111(1), 130-136. doi:10.1016/s0378-7753(02)00305-1
- Ratnakumar, B. V., Smart, M. C., & Whitcanack, L. (2010). Storage Characteristics of Lithium-Ion Cells. doi:10.1149/1.3393865
- Takeno, K., & Shirota, R. (2006). Capacity Deterioration Characteristics of Li-ion Batteries for Mobile Terminals. NTT DoCoMo Technical Journal, 7(4), 66-70.
Update
Further research I've found. Most of it is more relevant to electric cars than phones, but the principles should apply.
Extending Battery Lifetime by Avoiding High SOC
Summary: only charge a battery as high as you need it to extend the lifespan.
State-of-Health Estimation of Li-ion Batteries: Cycle Life Test Methods
Summary: The longest lifetime is observed for cells cycled with low peak currents and a narrow SOC range. In addition, high charge current is found to affect the cycle life profoundly. On the contrary, a moderate temperature increase did not result in a shorter cycle life.
Cycle-life model for graphite-LiFePO4 cells
Summary: At the low C-rates [Charge rates], experimental results indicated that the capacity loss was strongly affected by time and temperature, while the DOD effect was less important. At the high C-rates, the charge/discharge rate effects became significant.
Summary: It was found from the extensive cycling that the cycle life was shorter for the cell cycled in the higher SOC range, 60–70%, than the cells in the 10-20% range.
Overall summary: avoid charging the battery higher than you need it to be charged, don't charge it too fast (in less than an hour), and keep the battery cool especially while charging. There's also a suggestion in the last paper than the further you discharge the battery the more wear it experiences, but it's not clear from the abstract if that cell had the same total power supplied (ie lower discharge but more of them) or it just had less use.
Commentary
I've rarely charged my Pixel 4a battery above 80%. It's two years old and AccuBattery is reporting battery health is 95% - capacity is down from 3080mah to 2884mah, which is pretty good.
I'm interested in any other research based information people have found.
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