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…

What is a Battery and How Does it Create Energy?

A battery is a device that converts chemical energy into electrical energy. Batteries have two electrodes, an anode (the negative end) and a cathode (the positive end). Collectively the anode and the cathode are called the electrodes. What is positve and what is the negative terminal? It would be great to simply say that the anode is negative and the cathode is positive, however, that is not always the case. Somtimes the opposite is true depending on battery technology.

In between the battery’s two electrodes runs an electrical current caused primarily from a voltage differential between the anode and cathode. The voltage runs through a chemical called an electrolyte (which can be either liquid or solid). This battery consisting of two electrodes is called a voltaic cell.

Therefore batteries in effect create electrochemical energy. In order to convert chemical energy into electrical energy there is a chain of events that have to occur prior to the creation of electrical energy. Key to the creation of electrochemical energy in batteries is that electrical energy is injected into two chemicals in a solution. 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: the joining of a molecule (or molecule group) between two other molecules (or groups). Intercalation is the process of ions being pushed by electrical current into solid lithium compounds. Lithium is one of the chemical components used to create electrical energy in batteries. Lithium compounds have minuscule spaces between the crystallized planes for small ions to insert themselves from a force of current. Ionizing lithium 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. You could say if you use it you will lose it!

But what makes lithium good for batteries is that lithium is one of the metals in the alkali group (the other metals include Sodium, Potassium, Rubidium, Cesium, and Francium). Lithium is a highly reactive metal. Lithium has only one electron in its outer shell (two electrons in its inner shell), which makes it chemically “ready” to lose that one electron in ionic bonding with other elements. Lithium is used as a battery anode material (due to its high electrochemical potential). Electrochemical potential is the sum of the chemical potential and the electrical potential. The higher the electrochemical potential the better the electrical current yields. 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. One other core advantage that lithium has is that it is soft and bendable which allows for tight configurations in small cell designs (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, 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 X 4 cells in parallel equals 12 cells in total.

Until next time Dan Hagopian
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