Primary and Secondary Batteries

Batteries are broadly classified into primary and secondary batteries.

Primary batteries

Primary batteries are disposable batteries where the electrochemical reaction cannot be reversed. These batteries are used when the application requires a battery with a long shelf life (lower self discharge). For example your flashlight should stay in the shelf for a year and is expected to work when there is an emergency. Primary batteries are inexpensive and readily available.

Secondary batteries

These are rechargeable batteries where the electrochemical reaction can be reversed. Rechargeable batteries can be used again and again, and hence require proper maintenance. Although the initial cost is higher, have lower initial voltage and capacity, and not readily available compared to Primary batteries, these batteries are worth its cost when used for longer periods. For your robot, you cannot expect to get a new primary battery every time it dies off and replace it. Instead, use a secondary battery which can be charged and reused. 

Wet cell and Dry cell batteries

Most of the batteries available today are lead-acid batteries. Based on the type of electrolyte and the way it is implemented, batteries are classified as Wet cell, Gell Cell and Absorbed Glass Mat batteries.

Wet Cell

Also known as flooded cell, Wet cell batteries use liquid electrolyte and the gas produced during the chemical reaction escapes through the physical vents in the battery. Wet cells are the first rechargeable batteries used; but they are not extensively used today as they spill the liquid electrolyte when inverted (sulfuric acid) and can damage the parts around it. Most car batteries use wet cell batteries; although bulky and dangerous, wet cell batteries are cheaper compared to other variants available.

Dry cell

A dry cell uses electrolyte in the form of a paste which does not spill out, even when inverted. There are many kinds of dry cell batteries available, and the most common ones are the Gel batteries and Absorbed Glass Mat (AGM) batteries using VRLA (Valve regulated lead acid) technology. Gel batteries use a gel like electrolyte, whereas AGM batteries uses a sponge like mass of matted glass fibers which absorb the electrolyte. Although expensive, these cells store more charge and better than wet cells.

A third variant of Molten Salt battery is also available which uses molten salt as an electrolyte; both primary and secondary batteries can be manufactured using molten salt as an electrolyte which can provide high energy density and high power density.

Types of Robot Batteries

There are different types of batteries available in the market which can be either primary or secondary. With the advancement in battery technology, it is impossible to list and detail all the batteries available which would make this tutorial obsolete in a couple of days. Most common and readily available batteries are listed in the next few sections.


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