It is absolutely acceptable to only partially charge lithium-ion batteries, and doing so may even improve the longevity of the cells.
Battery University reports that the cycle life of a battery roughly doubles for every 0.1V decrease in the voltage of the cell.
When charging your phone at a level between 30 and 80 percent, the voltage is kept at a low level, which helps the battery last longer.
Long full charge cycles are far more detrimental to the life of Li-ion batteries than smaller but more frequent top-off charges.
The battery’s lifespan can be increased by up to two times if it is discharged to only 60 percent of its capacity rather than its full capacity before being recharged.
Although it is common practice, it is not advised that you charge your device while it is cradled during the day or overnight.
The most effective way to avoid parasitic loads is to turn off your device completely while it is being charged.
The battery is put under stress when exposed to high temperatures, which accelerates the rate at which it loses capacity.
After the first year, a cell that has been maintained at temperatures between 25 and 30 degrees Celsius (77 and 86 degrees Fahrenheit) should maintain 80% of its capacity.
The heat depletes the power stored in the battery.
Don’t make the mistake of charging your phone overnight with it tucked under your pillow, or of leaving it plugged into the dashboard of your car on a warm summer day.
It is better for the health of the battery to stop charging it at 80 percent than to charge it all the way to 100 percent.
The use of fast charging technologies should be limited to infrequent occasions and should never be left on overnight.