I have aToshiba Satellite laptop. It's used mainly plugged in. For those times I'd like to use it unplugged, I want to extend the battery's life as much as possible since this model laptop has a battery that is very hard to replace by the average user. Is it good policy to run it only on battery on occasion, or doesn't that matter anymore? I notice that when plugged in, the battery charges only to 80%. I suppose that's a protective feature. Thanks for your insight.