Battery School Pt.2

Primary vs Secondary battery - what is the difference?

In our previous class in battery school, we mentioned that battery technologies are divided into two categories: primary and secondary. Primary battery is the non-rechargeable type whilst secondary is the rechargeable alternative. Since the primary batteries are non-rechargeable and must be exchanged once they are expired, they are also called “disposable batteries”. All batteries are considered toxic waste and must be disposed of as electronic waste.

Both technologies have a wide range of sizes, from the standard AAs to coin cells to more odd sizes like N or AAAA. A big difference, however, is that secondary cells are usually assembled and sold as battery packs and are built into your devices, such as laptops or electric toothbrushes, whilst single cells like the alkaline AAA or AA batteries are used in products such as children’s toys.

The most common primary chemistries are alkaline and lithium manganese dioxide (CR), whilst the most common secondary chemistries are:

  • Lithium-Ion
  • Nickel-Metal-Hydride
  • Lead-Acid
  • Nickel-Cadmium

“Most secondary batteries are built in to devices, such as your phone.”

An important difference between the technologies is the expected lifetime. As explained earlier, primary has only one use and must be changed after it’s been depleted. The primary battery’s lifetime is that of how long it can power a device. As a secondary battery can be recharged after it has been depleted, its lifetime is counted in “cycles” instead. 

One cycle is from fully charged to uncharged and back to fully charged. To put it in an example, in the morning your phone is at 100% and at the end of the day it might be at 0-1%, you recharge it up to 100% during the night – this is one cycle in the battery’s lifetime. Cycles can range from 100 to more than 20 000*, but this is dependent on the kind of chemistry and usage.

To round it up

  • Primary batteries are non-rechargeable and counts as disposable.
  • Secondary batteries are rechargeable and can be reused as many times as its cycle life says.
  • Used batteries, primary and secondary, must be disposed as electronic waste.
  • Secondary batteries are most commonly sold as battery packs, meaning that the end consumer rarely interacts with them.

*Vanadium redox, or the vanadium flow battery, is said to have 20 000 cycles.

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