I don't understand batteries

Like so many rechargable batteries that I’ve bought over the years, the one in my laptop is slowly dying.

My phone battery is already almost pointless, and I’m sure that my iPod won’t be too far behind the pack. I suspect this is because I don’t know how to use batteries anymore.

I remember being told, ages ago, that one should always run a battery down as much as possible, then recharge it entirely at once. But batteries are like buter and margarine - what’s better changes every year, and I gave up trying to figure it out long ago.

So I guess i’m going to have to buy another laptop battery.