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I always read it was best to recharge your battery when it had about 20-30% remaining.
Plus, I thought the main reason the batteries degenerated was because of either heat, or due to the charger constantly charging it to 100%, then letting the battery fall down to 95% and then charging it back up, and those little cycles would always kill the battery.
Plus, the laptop will never let the battery drop below its critical voltage. With Lithium Polymer batteries, at least, if you drop below a certain voltage, your batteries are toast. They'll just puff up and won't charge again.
As for storing batteries, I believe it's best to charge the battery to about 60% and then keep the battery in a cool place. That's at least what is recommended with radio control lithium polymer batteries. I'm not sure how laptop batteries/lithium-ion batteries differ.
From my research and experience, 20-30% should be the minimum. Otherwise, depending on your charging rate, heat buildup might become an issue.
You're right about the storage. 60-70% charge is best, and keep them cool. It might be overkill, but I keep mine in the fridge for long term storage.
Short, frequent cycles don't hurt the battery as long as they don't heat it up. Whether topping off would heat up the battery would depend on the rate your internal charger uses.
IME with lipos and li-ions on a separate charger that monitors temperature the only time they heated up to any extent was when I was charging a very low battery and/or at a high rate. At what point the charger kicks in on a laptop would vary by design, I would think. It's purely speculation, but I would imagine the charger is designed to charge when the voltage and amps are still high enough that there wouldn't be much heat build up. Anyway, the point is that if your charger is designed right, it won't take so long to put back a 5-10% charge that heat becomes an issue. In and of itself, repeated charging cycles don't hurt the batt., but heat will.
I got a separate Universal MAHA C777Plus charger. I use it to recharge anything that has an internal lithium battery, instead of relying on internal chargers or wall warts. I use it for Cameras, MP3 players, laptops, bike-light battery packs and even lipos (although it won't fully charge them, it's safer and I can top them off on another dedicated charger). The newer models might even do lipos as well. It's a lot easier on all my lithiums. It's a good investment and I recommend it highly. They're about $40-50 at Thomas Distributing and it'll pay for itself in battery lifespan.
I used to do a lot of RC plane stuff, so I know what you mean about lipos, the same thing applies to hard-shelled lithium batteries, except they don't puff. They're vented and should contain a PCB, but the chemistry is the same.
