Here's the best tip for getting a battery that lasts forever:
NEVER leave the battery in unless it NEEDS to be in. Leaving it plugged in is like letting it constantly discharge and recharge which kills its lifespan....just use the AC adapter only. And you get cooler cpu temps when you take the battery out since it acts as a blanket to a certain degree.
No, with laptop batteries, it's impossible to "overcharge" them.
Don't charge the battery with the computer on unless you can't avoid this. The logic is that you want to have the battery hooked up to AC power for as little time as possible. Having your computer on draws more power from the battery making it take longer to charge.
I've heard it doesn't matter whether you start charging @50% or at 0% since Li-Ion batts don't have that problem with memory and whatnot.
Doing this, I think I've fully discharged and recharged my battery maybe 10 times in the last 8 months. Right now, I'm just hooked into the wall with my battery next to me in my backpack should I need to use my computer where there is no wall outlet.