How Batteries Work

Rechargeable Batteries

With the rise in portable devices such as laptops, cell phones, MP3 players and cordless power tools, the need for rechargeable batteries has grown substantially in recent years. Rechargeable batteries have been around since 1859, when French physicist Gaston Plante invented the lead acid cell. With a lead anode, a lead dioxide cathode and a sulfuric acid electrolyte, the Plante battery was a precursor to the modern-day car battery.

Non-rechargeable batteries, or primary cells, and rechargeable batteries, or secondary cells, produce current exactly the same way: through an electrochemical reaction involving an anode, cathode and electrolyte. In a rechargeable battery, however, the reaction is reversible. When electrical energy from an outside source is applied to a secondary cell, the negative-to-positive electron flow that occurs during discharge is reversed, and the cell's charge is restored. The most common rechargeable batteries on the market today are lithium-ion (LiOn), though nickel-metal hydride (NiMH) and nickel-cadmium (NiCd) batteries were also once very prevalent.


When it comes to rechargeable batteries, not all batteries are created equal. NiCd batteries were among the first widely available secondary cells, but they suffered from an inconvenient problem known as the memory effect. Basically, if these batteries weren't fully discharged every time they were used, they would quickly lose capacity. NiCd batteries were largely phased out in favor of NiMH batteries. These secondary cells boast a higher capacity and are only minimally affected by the memory effect, but they don't have a very good shelf life. Like NiMH batteries, LiOn batteries have a long life, but they hold a charge better, operate at higher voltages, and come in a much smaller and lighter package. Essentially all high-quality portable technology manufactured these days takes advantage of this technology. However, LiOn batteries are not currently available in standard sizes such as AAA, AA, C or D, and they're considerably more expensive than their older counterparts.

With NiCd and NiMH batteries, charging can be tricky. You must be careful not to overcharge them, as this could lead to decreased capacity. To prevent this from happening, some chargers switch to a trickle charge or simply shut off when charging is complete. NiCd and NiMH batteries also must be reconditioned, meaning you should completely discharge and recharge them again every once in a while to minimize any loss in capacity. LiOn batteries, on the other hand, have sophisticated chargers that prevent overcharging and never need to be reconditioned.

Even rechargeable batteries will eventually die, though it may take hundreds of charges before that happens. When they finally do give out, be sure to dispose of them at a recycling facility.

Next, let's take a look at battery arrangement.