cell phone battery 20%-80%

Charging your battery to full capacity less frequently, and not letting it run totally dry, can extend its life — somewhat. Putting less stress on the electrodes results in less degradation, and ultimately higher capacity for a longer period of time. it is possible to prolong the battery life by not completely charging and not completely discharging,” Mr. de Vries said. “So we’ll say stay between 20 percent and 80 percent or so.” The battery lifetime is “inversely proportional to the amount of lithium ions that you put in the electrodes.”

This is one reason Apple offers optimized battery charging on its iPhones, keeping the charge below 80 percent until you need the battery topped off. Android doesn’t have a similar system-level algorithm, but individual manufacturers like OnePlus and Asus have introduced their own optimization features.

Heat is another factor that negatively affects battery life. “Heat is the worst enemy of batteries,” according to Battery University, a repository of battery science information maintained by the battery-testing company Cadex. “Lithium-ion performs well at elevated temperatures but prolonged exposure to heat reduces longevity.”

According to Mr. Purdy, heat is especially a problem when you’re wirelessly charging.

“Depending on a number of factors — alignment, sophistication of charging base, phone cases, interference — your charger can end up delivering as low as half of the current it draws into your phone,” he said. “Where current meets resistance, there is heat.” 

By Nick Guy

Mr. Guy is a senior staff writer at Wirecutter, a product recommendation site owned by The New York Times Company.

• Sept. 4, 2020