How Many Cells Are in a Battery?

Question from a reader: "How many cells are in the Toshiba Satellite M105-S3041 Laptop Battery? The battery is for a Toshiba Satellite M105-S3041 and its technical ratings are 10.8 volts 8800 mAh, Lithium Ion."

The question from the reader is a great question for it gets to the heart of battery manufacturing and begins to unravel the power of a battery. The answer is simply: 12 cells. But what does the answer mean and how does the number of cells relate to the overall value of a battery? Let's find out...

How Does A Battery Create Energy?

A battery is a device that converts chemical energy into electrical energy. Batteries create electrochemical energy by a chain of events that have to occur prior to the creation of electrical energy. Electricity is introduced into a battery via a charger. The charger acts as a conduit of the pushing electrons that are forcing their way into the chemical lithium. This charge process involves intercalation where electrons join with other molecules in the lithium's minuscule spaces between the the lithium's crystallized planes. Electrons are in essence ionizing lithium which loads the crystal planes to the point where they are forced into a current flow. Intercalation replenishes, in effect, lithium but the net result of ionization is the ultimate depletion of the lithium reactive property.

But what makes lithium good for batteries is that lithium is a highly reactive metal. Lithium has a very high electrochemical potential. In some lithium-based cells the electrochemical potential can be five times greater than an equivalent-sized lead-acid cell and three times greater than alkaline batteries. Lithium is also pliable and bendable allowing lithium to fit in tight configurations (perfect for in small cell designs in PDAs. Laptops, Cameras etc...).

What Type of Lithium Cell is Used in Laptops

Now this brings us to battery cells and our original question from the reader. Lithium based battery cells are good but there are a variety of lithium based battery cells. For example the lithium based cell identified as 18650 is one of the most common battery cell on the market for laptops. 18650 is manufactured by many manufacturers including many private branded companies to public companies like LG, Sony, Sanyo, Samsung, and Panasonic.

18650 is a 3.6V cylindrical Li-Ion cell. 18650 has no memory effect (distinguish between digital memory effect) and longer storage life than NiMH battery cells. 18650 is light weight and has a high energy density. It is in effect perfect for building batteries for laptop and other portable power devices.

The additional technical specifications for the 18650 battery cell include:

• Nominal Voltage Average 3.7 V - the concept of nominal voltage is that voltage range exists depending on the number of cells in the battery.
• Nominal Capacity - 2200 mAh (above 2200 the stability of lithium based cells is called into question)
• Max. Charging Current - 2.4 Amps Max.
• Max. Discharging Current - 4.6 Amps max.
• Dimensions (DxH) 18.3 mm (Max 18.4) x 64.9 mm (Max 65.1)
• Weight 46.5 g (1.64 oz)
• Internal Impedance Internal Impedance: less or equal to 90 ohms
• Cycle Performance is 80% of initial capacity at 300 cycles

Now as stated above the reader asked how many cells were in the Toshiba Satellite M105-S3041 Laptop Battery? The battery is rated at 10.8 volts and a capacity of 8800 mAh.

As I mentioned above the nominal voltage average is 3.7V. Some manufacturers may use 3.6V and some may use 3.7V. In the case of a laptop battery with 10.8V the nominal voltage rating used is 3.6V. Thus if we divide 10.8V by 3.6V we get 3. Thus 3 cells in a series. We also know that the batteries capacity is 8800 mAh. We know the nominal capacity is 2200 mAh. Therefore if we divide 8800 mAh by 2200 mAh then we get 4 in parallel.

Therefore we have: 3 cells in series multiplied by 4 cells in parallel equals 12 cells in total.