Have you ever wondered what’s inside notebook batteries? Hopefully, you’ve resisted the temptation to crack the notebook battery open, since that not only voids any warranty you have, but can also be quite dangerous. Since our trained technicians have opened several notebook batteries in the safety of our lab, we thought we should share what we found.

From the outside, notebook batteries appear to be one solid mass, but notebook batteries actually consist of three component parts covered by a plastic shell or wrapper. The largest “ingredient” by weight and volume are the energy cells that generate power, but you’ll also find a small printed circuit board (PCB) that controls how the notebook battery cells are recharged, as well as the connector that interfaces with your notebook.

Most new notebook batteries consist of 6, 9 or 12 lithium ion cells, carefully matched together because of their identical impedance levels. (Impedance, which is measured in Ohms, is a fancy word for resistance.) The notebook battery cells are wired both in series and in parallel to provide the voltage and current flow required by your laptop.

In case you’ve forgotten, parallel connections result in no change to the overall voltage of the circuit, while series connections multiply the voltage by the number of cells. The diagram below illustrates the point. The top drawing shows a parallel connection of four 1.5 Volt cells, while the bottom drawing shows similar cells wired in series. (In this case 4 x 1.5 Volts = 6 Volts.)

The electrochemical characteristics of a Lithium Ion notebook battery dictate that an individual cell carries 3.6 V. That’s why most notebook batteries have a voltage rating that is an even multiple of 3.6 – usually 10.8 or 14.4.

The cells in notebook batteries need to stay connected in order to maintain the flow of electricity. This requires the terminals on a notebook battery be soldered together. Many notebook battery manufacturers insert the connected cells into a plastic sleeve, which they then seal at the seams with a special ultrasound machine. Their goal is to keep the cells tightly and densely connected, since the notebook battery pack has to meet precise tolerances to fit inside your laptop.

At one end of the notebook battery pack is a small circuit board that electronically senses the charge and discharge levels, as well as the overall state of the notebook battery, i.e. how much charge is left. This component is absolutely critical to the notebook battery pack; without it the lithium ion cells would overcharge and overheat.

Finally, there is a specially designed connector that provides pathways both for the electrons to flow out of (and back into) the notebook battery pack, as well as for the PCB to communicate with the laptop microprocessor.

When everything is packed snugly together inside a plastic casing, the manufacturer slaps a descriptive label on the outside and sends it off to the market.