With my previous laptop, I was sort of lazy, and just kept it plugged in as I was mostly using it at home.. Well, it was no surprise that the battery died a long time ago (the laptop was bought in early 2008), and then I had no choice but to keep it plugged in. I did think about buying a replacement battery, but I never did, and eventually (and recently), I had to buy a whole new laptop, so there was no need for a new battery.
Now that I have a lovely new laptop (with a lovely new battery), I've been trying to only keep it plugged in to charge the battery, and then using it until the battery needs charging again.
But I remember reading an article about mobile phone batteries, and how to make them last as long as possible - I'm not referring to the battery life in daily use, but the actual time you can keep using a battery, until you have to replace it or buy a new phone. (Sorry, I don't have a link to the phone battery article, and I think it was in Finnish.. If you're interested in that topic, google it..)
I decided to google for a similar article about laptop batteries, and I found this: Keeping Your Laptop Plugged in All the Time Will Kill Its Battery Faster (Sept-2013, Wired). Quoting the key part;
Cadex Electronics CEO Isidor Buchmann told WIRED that ideally everyone would charge their batteries to 80 percent then let them drain to about 40 percent. This will prolong the life of your battery — in some cases by as much as four times.
(Read the whole article, though. It's not very long.)
I will definitely try and make it a habit, to keep checking that battery status icon..