As of the date of this writing there were 19,300,000 results in a Google search for the keyword laptop battery. On the one hand that is great if you are in need of one but at the same time overwhelming. How do you know what to buy, from who to buy, and what you even should be looking for when buying a laptop battery? I have identified seven categories a person needs to be informed about when going out to make a purchase for a new battery and they include: Part number, Make, and Model; and Chemistry; and Capacity; and Voltage; and Watt Hours; and Number of Cells; and finally the Retailer, Price and Warranty.

**Part Number, Make, and Model**

Essential to the purchase of your new laptop battery is the part number. A part number is a unique identifier that is assigned to a part to simplify referencing and to unambiguously define a part within a single manufacturer. The part number above all is what needs to be known before going to buy your battery. Secondly the make and model are next most important part identifiers you must know. The make is the manufacturer (e.g. Sony, HP, Dell). The model is a multi-component word that includes the line and actually model number. For example the Sony VAIO VGN-FZ90S is an example of a sony made laptop that is part of the VAIO series and which has model number VGN-FZ90S.

Most laptop’s hold this information within your computer’s system info. To access this info go into the properties of your computer and view the model information. The battery’s part number can be found on the battery itself.

**Chemistry**

Most laptops now require a lithium based battery chemistry. You cannot choose your chemistry type for most batteries. It is still good however to know which chemistry type yur battery requires.

**Capacity**

Capacity also known as runtime Battery capacity quantifies the total amount of energy stored within a battery. More capacity equals a longer runtime between battery charges. Battery capacity is measured in amperes, which is the volume of electrons passing through the batteries electrolyte per second. A milliAmp hour (mAh) is the most commonly used notation system for consumer electronic batteries. Note that 1000 mAh is the same as 1 Ah.

When buying a battery knowing how much capacity you may need depends on: how much you want to spend, how often and how long you use your laptop on battery power, and what applications you my be running off the battery’s power. The higher the capacity the more money you will spend, so if you need the longer runtime’s or you use applications that require more battery juice then buy the higher capacity.

**Voltage**

Volts – or V – is an electrical measurement of energy potential. Mathematically voltage is commonly measured by V= I x R; where V=Voltage, I=Current, R=Resistance. Voltage can also be defined as Electrical Potential difference – a quantity in physics related to the amount of energy that would be required to move an object from one place to another against various types of force. In the fields of electronics the electrical potential difference is the amount of work per charge needed to move electric charge from the second point to the first, or equivalently, the amount of work that unit charge flowing from the first point to the second can perform. A battery contains four unique types of voltage measurements. Each voltage measurement type residing in a battery effects battery life.

- Float Voltage – is battery voltage at zero current (with battery disconnected).
- Nominal Voltage – is battery voltage range 3.7V, 5.2V, 10.2V, 12V etc that says that a voltage range exists depending on the number of cells in the battery. For example a 12 Volt battery is made of 6 cells and has a Float voltage of about 12V.
- Charge Voltage – The voltage of a battery while charging.
- Discharge Voltage – The voltage of a battery while discharging. Again, this voltage is determined by the charge state and the current flowing in the battery.

For laptop batteries the most common voltage measurements are: 7.2V, 9.6V, 10.8V, 11.1V, and 14.4V. Since you cannot choose the voltage measurement for your laptop go with whatever measurement is closest to your original battery. Remember nominal voltage allows for slight deviation from the original but you cannot use a 7.2V battery if it requires 14.4V. The best example would be a 10.8V battery could be used with an 11.1V battery.

**Watt Hours**

Whr, Watts, Volts and Amperes are basic units of measure for a DC (Direct current) power supply. A battery, for example, is a direct current power supply and the combined measure Volts x Amps = Watts. Watts are important because watts represent the electrical energy spent by a battery (power generator) and used by an electrical device. Watts in effect is the measure of the amount of work done by a certain amperage (amount) of electric current at a certain pressure or voltage. Watt hours are measured by multiplying volts and capacity together (and commonly rounding up).

**Number of Cells**

The number of cells is important since the more cells contained in the battery the higher the capacity will be. To determine the number of cells in your laptop battery you need to have some general idea of what cells are being used in your battery. The most common battery cell is the 18650 and is manufactured by LG, Sony, Sanyo, Samsung, Panasonic and many others. The 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.

Specifically the 18650 battery cell has a nominal voltage average of 3.7 V. It has a nominal capacity of 2200 mAh. It has a maximum charge current of 2.4 Ah and a max discharging current of 4.6 Ah. Its dimensions (DxH) are 18.3 mm (Max 18.4) x 64.9 mm (Max 65.1). It weighs 46.5 g (1.64 oz) . It has cell cycle performance of 80% of initial capacity at 300 cycles. All in all the 18650 is a very good battery cell.

Using this common laptop battery cell as our base you can determine the number of cells in your laptop battery by doing the following. Divide the battery’s stated voltage by the 18650’s nominal voltage to get the number of cells in series and divide the battery’s stated capacity by the 18650’s nominal capacity to get the number of cells in parallel. Then multiply the results of the series and the parallel to get the total number of cells in the battery.

**Retailer, Price and Warranty**

Once you have all the above information now it is time to pick and choose a retailer to buy from. When choosing a retailer to buy a laptop battery from take into consideration the retailer’s reputation, the price, the warranty, and the return policy. Be sure to chat or speak with one of their representatives if you have questions. Be smart about where you buy from and only buy from a reputable retailer. With batteries you never want used and you always want to be sure that is a problem arises the retailer will be there to make it right.

Until next time, Dan Hagopian – www.batteryship.com

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