Dry cells and rechargeable batteries

A Voltaic cell full of liquid is awkward to carry and can spill. So today we mostly use dry cells, the kind in a TV remote.

It is called dry because the electrolyte is not a liquid but a thick, moist paste. That's the only reason for the name.

A dry cell is single-use: once its chemicals are used up, it must be thrown away. That's why rechargeable batteries are used more and more.

A rechargeable battery can be charged and used again many times, which cuts waste and saves money. They come in every size: in watches and phones, laptops and tablets, and big ones that run inverters or drive electric vehicles.

But they don't last forever. After being charged and used many times they slowly wear out. That's why a phone needs charging more often after a year or two.

Today's most common rechargeable battery is the lithium-ion (Li-ion) battery, found in almost everything that uses batteries. It needs special metals such as lithium and cobalt, which are mined in only a few parts of the world. So countries are racing to secure supplies, recycle old batteries and develop new technology.

The next big step may be solid-state batteries, which replace the liquid or paste electrolyte with a solid material. They would be safer, charge faster and last longer, which matters as the world moves to cleaner sources of electric power.