Don't leave it fully charged. Similarly, lithium-ion batteries don't need to be charged all the way to 100%. In fact, they'd prefer not to beso the 40%-80% rule you heard is a good guideline. When possible, keep it in that range to prolong its life as long as you can. And, if you do charge it to 100%, don't leave it plugged in. This is something most of us do, but it's another thing that will degrade your battery's health. If you need to charge it overnight, use something like the Belkin Conserve Socket to stop it from charging after it's full.