Okay, my laptop is at 12 % as I typed that. Let's see if it can last long enough for me to type this. My battery is draining, REALLY fast. Like, I unplugged it from my sister's room at about 25 percent, and it's almost dead. It drained from 15 to 13 percent in a minuet or two, and that power settings is on eco. It's a toshiba sattelite laptop, and I THINK it's still under warrenty.
And yes, we're one of those people who leave their laptop plugged in about 24/7, and leave it ON 24/7. Trust me, if I was able to use it I wouldn't, however I'm letting me sister use it until her laptop is fixed. Oh look, it died. And I typed this in a few minuets.
Leaving it plugged in all the time and never exercising the battery at all generally isn't good for them either. A rechargeable battery shouldn't be drained dry, but a 50%-60% discharge every month or two can help it.