Any ways to save an already-bad laptop battery?

My laptop battery is almost 2 years old, and even when it's fully charged it can only last no more than 20 minutes. I plan to use it until it dies, but I would like to know what should I do to prolong the life of this already-bad battery. I think I'll leave it plugged in at all times. I know this will make it weaker, but my previous battery got toast because I used it until it had 0% charge in it, then left it uncharged overnight then next morning, I discovered it was broken. The reason was because I did not promptly charge it when it was completely drained. I don't want the same thing to happen to this one. I'm just afraid that if I unplug the adapter, the battery will be discharged after 20 minutes and I'm not at home to replug it then it will die just like the old one. Any ways to save this pathetic battery?