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How a lead-acid battery works

With the massive explosion in the use of mobile devices like laptops and cellphones over the last decade, lithium-ion batteries have garnered a lot of attention. So it’s easy to forget that old stalwart, the lead-acid battery. This 19th century technology is what starts your car every day, and there’s a good reason for that, as explained in this YouTube video.

The interior of a lead-acid battery, like your car battery, is made up of multiple cells with alternating lead and lead-oxide plates. These are very heavy, dense materials, but they are abundant and highly-conductive. Current flows from the lead-oxide cathode, to the lead anode. Electrons are passed to the lead-oxide plate, and both plates are slowly converted to lead sulfate (from the sulfuric acid).

Multiple cells are needed inside a lead-acid battery to give the unit sufficient power. These batteries are high in power density, and release that power quickly. Perfect for starting a car, but not so much for other uses. Electric cars use lithium-ion batteries because those cells are ideal for “deep discharge.”

Deep discharge is basically just draining a battery over time until is is empty, or nearly empty. If you do that to a lead-acid battery more than a few times, it will stop charging as lead sulfate coats the plates. More modern batteries don’t have that problem, but you lose the quick discharge ability.

A lead-acid battery could be modified to act as a deep cycle, but the plates would have to be thicker, and spaced farther apart. The casing would also have to be more spacious to accommodate the inevitable build-up of lead sulfate. This heavier version of a lead-acid battery would have lower current, and that’s why we use different technologies in different circumstances.

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