Do Batteries Degrade Over Time. Do lithium-ion batteries degrade over time. Heres why batteries degrade over time.

Degradation of these batteries is mostly brought about by their exposure to heat. Electric vehicle batteries have a second life after 100000 to 200000 miles on the highway Graham explained. So your efficiency goes down.
Storing your device with charge over 80 or under 20 or leaving the device plugged in to charge after it is charged will degrade your battery Scientists have found that there is nothing you can do to prevent damage due to use over time but your best course of action is charging up to 80 using the device down to 20 and then charging again.
For LiOn batteries its best to store them at a capacity between 50-80 if you do that you wont notice any degradation at all over a short period and even over a long term say one year the degradation should be minimal say upto 10. The working battery has a certain remaining life. When the battery performance of an electric car drops to 70 or lower its second life begins. The common complaint associated with the smartphones is the rapidly discharging battery that degrades with time.
