Meh, if undervolting was really that effective, they would've done it to the laptop as they shipped it. Modern laptops are tougher, since they have to focus on finding more effective ways to utilize the battery, rather than making stronger batteries. The same goes for unplugging your battery/charger while the battery is full gives a longer battery life - if you see a 'using AC power' thingy on the taskbar, Windows has already done that for you.
However, the undervoltage & 'don't overcharge' principles still applies to most rechargeable batteries, old/cheap cell phones included.
Disclaimer: Any sarcasm in my posts will not be mentioned as that would ruin the purpose. It is assumed that the reader is intelligent enough to tell the difference between what is sarcasm and what is not.