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 polymer lithium-ion batteries, though nickel-metal hydride and nickel-cadmium batteries were also very prevalent.

When it comes to rechargeable batteries, not all batteries are the same. 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 would quickly lose capacity. NiCd batteries were largely phased out in favor of NiMH batteries. These secondary cells have 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 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 rechargeable batteries 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.