This one might be a little bit OCD, GeekDads, but the technical details are at least a little bit interesting, so bear with me. You see, I have an LED flashlight that I’m generally quite fond of. The light uses lithium cells (18650s) that I harvested from an old laptop battery pack, so it lasts forever, and it puts out a startling amount of light. The only thing about it that I don’t/didn’t like was the fact that it was a multi-mode light — i.e. by quickly tapping the switch, the light cycles between low, medium, high, and (ultra-annoying) blinking mode. The low, medium, and high modes are nice, though the switch is a little too sensitive and prone to switching modes by accident. That last mode though — the seizure-inducing blinking mode — was a deal breaker.
Now, an old-school incandescent flashlight consists of a bulb, battery, switch, and some wire, so there’s not much there to tweak or tinker. A modern LED flashlight, on the other hand, includes a little circuit board that consists of a current regulator and a microcontroller.
A partially disassembled laptop battery (photo by Roy Wood)
If you’ve owned a laptop for a few years, you’ve no doubt encountered the problem that the battery eventually loses its ability to hold a charge. Generally what happens is that one or more of the cells inside the battery pack degrades to the point that it cannot be recharged, and the entire pack loses its effectiveness. At this point, your choices are to buy a new replacement pack, or put on your hardware hacking hat and safety glasses, and start taking things apart.
Now, before you start tearing things apart, note that the lithium cells in a laptop battery can contain a lot of power, and you can hurt yourself or set things on fire if you’re not careful. Sound scary? It should! And if so, then perhaps you should content yourself with just reading through this posting, rather than messing around with things yourself. Either way, on we go.
As you can see in the image on the right above, a laptop battery pack consists of a number of individual cylindrical cells. These cells look a lot like a standard AA alkaline battery, but they’re actually a bit longer and wider than a AA battery. These are lithium cells which go by the part number “18650″ (this is usually printed on the side of the cell, in fact).