Why does every laptop manual suggest that users deep cycle their batteries every month or so? Actually, it's not only laptops, but almost all battery operated equipment. This is not a good practice.
Deep cycling, for those of you not familiar with the term, is the act of discharging your batteries to zero charge (or as low as you can get them) before charging them again. This was once done to remove what were called "memory effects" from batteries - a situation that prevents the batteries from being restored to their full capacity.
The problem with deep cycling is that it seems to actually ruin most batteries. A few years ago, I read a whitepaper from a battery manufacturer that provided charts and other detailed scientific studies to show that it is best never to take a battery below about 50% of full charge. In fact, the lower you go below that, the more you will damage your batteries and shorten their lifespan.
I have confirmed this fact by my own observations and tests (I've built devices to try to "save" bad batteries). In my experience of deep cycling, I've often managed to ruin a wide range of batteries from laptops to camcorders to power drills in as little as ten recharge cycles. On the other hand, I have batteries that are now over 1000 recharge cycles (and some are using really low quality batteries) and still going strong (cell phones, outdoor lighting, toothbrushes, etc.).
So what's the truth? I must say that I'm no expert in batteries. It is possible that I'm somehow wrong here. But, I do know what I've observed to be the fact. The question, however, remains: should you really deep cycle your batteries, or should you save that act for when you know a battery is suffering from a memory effect, and you need to take desparate action to see if you can save it from total ruin.
One other thing to ask: is it possible there is a huge battery "scam" going on here? After all, it can cost a lot to replace batteries for camcorders, laptops, cell phones, and other devices.
Of course, that takes me to the subject of what I'm almost certain is a battery scam. But, I'll save that topic for another blog.