Determine How Many Cells In A Battery Pack

Working with batteries and battery packs is sometimes an overwhelming task if your new to it. As a blogger and battery store owner, I get alot of question about batteries. Such as, how many cells in a battery, comes up frequently. How many cells do I need to make a battery pack with a certain voltage. 

Math For Cells In A Battery
The math is actually not that difficult. In fact is only a simple division problem. Lets do a couple examples with the following formula. Use the tables below to get the voltage and cells chemistries used in your battery packs.

Battery Voltage / Cell Chemistry Voltage = Number of Cells
Cordless Phone Battery: 3.6V Ni-CD Battery / 1.2V Ni-CD voltage = 3 Cells
Airsoft Battery: 9.6V Ni-MH Battery / 1.2V Ni-MH voltage = 8 Cells
Laptop Battery: 11.1V Li-Ion Battery / 3.6V Li-Ion voltage = 3 Cells (Actually 6 cells) this is a series-parallel configuration.

I will be explaining in an upcoming post how to determine series-parallel vs series configurations. When to use them and how they work.

Device Cell Orientations and Chemistry Voltages
The table below will help guide you with common battery pack orientations. It can also be used to help you build custom battery packs for your do it yourself project. You may decide that you need a similar pack and need to know how it is constructed. If I have missed any, use the comments to ask me how its built. I would be happy to explain any configuration.

Common Device	Amount of Cells (Depends on Voltage)	Cells Used	Cell Configuration
Airsoft Battery	6 – 12	SubC	Series
Airsoft Lithium Battery	3 – 6	Li-Polymer Packs	Series or Series-Parallel
Cordless Phone	2 – 4	AA, AAA, 2/3A, 4/5A	Series
Laptop (External)	6 – 12	18650	Series-Parallel
Laptop (Internal)	6 – 12	Li-Polymer Packs	Series-Parallel
Power Tool Battery	7 – 12	SubC	Series

 

Common Chemistries	Cell Voltage (Nominal)
Alkaline	1.5V
Ni-CD (Nickel Cadmium)	1.2V
Ni-MH (Nickel Metal Hydride)	1.2V
LiFePO4 (Lithium Phosphate)	3.2V
Li-Ion (Lithium Ion)	3.6V / 3.7V
Lithium (Primary)	3.0V
Silver Oxide	1.55V

Still need more information on battery chemistries. A simple google search will find you everything you need but I actually like this article from Battery University. Whats the Best Battery, its explains the advantages and disadvantages of battery chemistries, their charge and discharge characteristics and best suggested application.

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