This is a very good read and a very good subject.
I have 2 batteries. One is always in my laptop and one is a spare that I have only used once or twice. I will discharge the spare to 40% and put it in the fridge. Just to test things out. I will leave the one in the laptop where it's at.
Personally, I don't think it really matters. We buy laptops to use them. If the batteries go dead and can not be charged - recycle them - then purchase new ones. I mean, you just spent 1.5/2.0K on a laptop. Whats another 50 bux for a battery?
FYI - there will always be replacements. Dell has a tendency to use the same battery design through several generations of it's laptops. That and if they did ever stop making them, a third party will have them.