The battery also contains an extremely important electric circuit, which assures that the battery functions normally and safely. This circuit is mainly composed of a transistor (FET- Field Effect Transistor) that kills everything should the tension of the charge exceed the nominal value of 0.1 V, as well as a fuse that blows if the temperature approaches 90 degrees C. Several types of fuses are used.

Certain fuses blow in a permanent manner once the filament is destroyed while others can be reactivated. We can also find a switch that reacts by cutting the current if the internal pressure is too high (more than 10 Bars). The circuit, which is present on a battery with several cells, also surveys the tension on each cell and the tension between cells. Its function is to prevent any over-discharge by cutting the current if it goes to below 2.50 V/cell.

Danger Will Robinson, Danger!

Manufacturers’ biggest fear remains that static electricity or a defective charger could harm or corrupt the electric circuit. Such damage could jam the fuse to the ON position, without the user being aware of it. Basically what would happen is that the electric circuit no longer carries out its primary function, which is to cut the current when the conditions required for it to function become hazardous. This may not happen often, but it reinforces the necessity of using the charger provided by the manufacturer, as using a different – or faulty – one is exactly what can lead to the conditions for an exploding battery.

Laptop battery manufacturers guard their secrets a lot more closely than other battery makers, and thus one battery can be significantly different to another, which is why Charger A should not be used with Battery B.

Battery combustion

There are several rules and standards when it comes to manufacturing Lithium-ion batteries. Nowadays the main one is the IEEE 1625 standard. This standard was agreed in April 2004 by some of the big names in the industry: IBM, Dell, Hewlett Packard, Compal, Samsung, Sony, Motorola, Texas Instrument and more.

Called the “Standard for Rechargeable Batteries for Portable Computing” label, these standards regulate the fabrication and design of these batteries. They also dictate quality control by imposing certain minimum criteria. The aim of the IEEE 1625 was clearly laid out as “more control in order to minimise the risks of thermal or mechanical shock, vibrations and other stresses.”

Some will notice that 2004 is a date relatively late in respect to the birth and evolution of laptops. There were already standards in place before this, but these had the disadvantage of being concentrated on the cells and omitted the packaging and the electronics surrounding the battery, or vice versa – in other words, they were not comprehensive standards. IEEE 1625 brought all of these different standards for different elements of the battery together under the one umbrella to ensure a uniform code across all reputable battery manufacturers.