How to prolong battery life

Gee… really? I just received tech news from HP and stuck in this article. It says that the best method of storing recharged battery when it’s in 40% charged. I always store all my recharged batteries at full charged. My kid’s PSP & DS, AA batteries for Wii’s controllers…
In my experience, fully charged PSP battery stored on Sunday can be played around 3 – 4 consecutive hours on the next Friday. Fully charged AA batteries stored inside the Wii’s controller will only left 3 bar after 5 days. Umm… I have a ritual of charging all drained batteries on Sunday after the kids use them all. Drained? yes for sure. They always force the console on after auto shutdown when the battery indicator flashes. I don’t know how, but it gives them a minute or two’s additional playing time. The article said it should be charged when it still 10 – 20%. Hehehe…
So, how’s yours?