Primary Batteries for Robots

Leclanché Cells

The wet cell invented centuries ago, contains a solution of ammonium chloride as an electrolyte and carbon as cathode. These were the first commercial batteries available and the chemistry of Leclanché cell was later adopted to invent dry cells.

Zinc Carbon Cells

Also known as Carbon-Zinc cells are the direct descendents of Leclanché cells. Ammonium chloride and Zinc chloride in water acts as an electrolyte; Carbon rod and an electrolyte acts as positive and negative electrodes. Carbon-zinc cells have a low shelf life, bad performers in varying temperatures and high resistance with usage. However they are inexpensive and readily available which makes it a choice of cell for cheap low quality devices.

Zinc Chloride Cells (Zn/Cl2)

A better version of Carbon-Zinc cells with Zinc chloride as electrolyte. Compared to Carbon-Zinc cells, they have higher performance in varying temperature, better shelf life and almost the same cost. Higher energy density makes them an ideal replacement for Zinc-chloride cells to power high drain devices.

Alkaline Cells (Zn/MnO2)

Alkaline cells use Potassium hydroxide as an electrolyte and most of your remote controlled toys, digital clocks normally have an alkaline cell inside;. These are the best use-and-throw cells available which are economical, have a long shelf life and higher energy density compared to Zinc carbon and Zinc Chloride cells and hence they cover more than 50% of consumer market today. If you need a quick replacement for a remote (read it as any low-current draw applications), then alkaline batteries serves best. They have a long shelf life, lower internal resistance which remains the same till the end of battery life, better performance at varying temperature and a steady voltage droop. Although they can withstand moderately high discharge current levels, they are pricey when compared to Zinc chloride and zinc carbon cells.

Mercury & Silver Oxide Cells

Also known as Zinc-mercury cells use mercuric oxide as a positive electrode and zinc as negative electrode; potassium hydroxide is generally used as an electrolyte. These cells are used in devices which require high energy density and a flat discharge curve and are generally available as button cells. Zinc silver oxide cell is another variation which uses silver oxide instead of mercuric oxide and their nominal terminal voltage is slightly higher than mercuric oxide cells. Since usage of heavy and toxic metals like mercury and silver is restricted in many countries, these cells are getting outdated and lithium cells are taking over their position.

Lithium cells

Lithium based cells are recently developed and a lithium primary cell uses a lithium metal or a compound as a positive electrode. The most common lithium based cell available is the Lithium-manganese dioxide cell which has higher energy and power density, long shelf life, efficiency, and discharge performance compared to alkaline cells. Lithium manganese cells are available in a variety of shapes from button cells used in quartz watches to typical cylindrical batteries used in flash lights. Their small size and light weight with high energy density make them ideal for high drain applications.

For a robot, it is always better to use a rechargeable battery. However if you ever require to use a primary battery, then the best choice is a lithium manganese dioxide cell (or battery). Zinc-air cells are a new advancement in battery industry with high energy density. They can stay on shelf for years before exposed to air; however they have a very low working life once they are exposed to air with low power density and are almost not suitable for robots.

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