A lot of folks that say to keep lithium ion fully charged are usually mis-informed on the different handling requirements of various battery chemistries, but some out there may be purposefully spreading mis-information to create additional demand for new devices. The reason I say this is: Take a look at the voltage of a fully charged laptop or cell phone battery. Chances are that the voltage at 100% charge is over 4.2 volts. I’ve seen my devices, both my XPS and Droid Turbo as high as 4.4 volts per cell, which is dangerously high and bordering on Thermal Runaway. Lithium ion batteries should never be higher than 4.2 volts per cell, and actually shouldn’t even stay at that voltage for very long if you want it to last more than a couple years. Since limiting the charge on my XPS to 74%, which is 4.0-4.1 volts per cell, battery degradation has stalled at 95.7% of design capacity, and this machine is going on 3 years old. It lasts just as long on a charge as the day it was new (actually better with TLP, so at least since I started using TLP tweaks).
General guidelines for lithium ion batteries are:
- Keep charge between 20-80% when possible. OK to go out of range occasionally, just keep it brief.
- Keep the battery cool. Temperatures above 85 F dramatically increase degradation.
a. But not too cool. Do not charge when below freezing, as lithium plating can occur and permanently reduce capacity.
- Minimize physical stress. Do not charge a puffed pack. Discharge and replace.
Electric car batteries are usually the same chemistry as laptop batteries (the Tesla Model S and Model X actually using 18650 cells, just like older laptops), and their batteries last upwards of 10 years without significant degradation simply because they keep the batteries cooler and don’t go above 4.2 volts per cell, many only going to 4.1 volts at full charge. For this reason, I second the ability to adjust the charge profile, as this is a must-have feature for me to switch to a Librem from my XPS.