Battery

An electrical battery is a combination of one or more electrochemical cells used to convert stored chemical energy into electrical energy. The type of electrical current produced by a battery is direct current. meaning it flows in a single direction. Because of this, batteries will have a positive and negative end, and more often than not, must be connected in the right direction to properly power a device.

There are two broad categories of cell
 * Primary Cell - Once exhausted, power cannot be readily restored to the battery by electrical means.
 * Secondary Cell - Also know as 'rechargeable', can be recharged by supplying a voltage. No battery is infinitely rechargeable and over time will lose capacity.

Primary cells are most commonly used in devices with low current drain, used intermittently, or are far away from alternative power sources.

Types

 * Battery primary cells
 * Battery secondary cells

Capacity
A batteries capacity is the amount of current it can supply for a given amount of time, and is typically measured in milliamp-hours. A battery that is 500mAh can supply 500mA of current for one hour, 250mA for 2 hours or 50mA for 10 hours.

Discharge Rate
Discharge rate of batteries is often referred to in terms of C. 1C is equivalent to 1A/Ah, thus for an 800mAh battery a 1C discharge rate is 800mA, a 2C discharge rate is 1.6A, etc.

When designing batteries as part of a project, you should pay close attention to both capacity and maximum discharge rate. In general, it's advisable to limit the maximum continuous current draw from the battery to no more than about 1C, even if you don't need a whole hour of capacity. If you want to discharge batteries quickly without killing them, consider cooling them (e.g. in RC cars, placing airflow / heatsinks on the batteries).

Note that often the rated mAh / Ah on a battery label is determined at a specific rate of discharge (usually for a 1 hour discharge of the whole capacity, or 1C). In general, a lower discharge rate (<1C) can yield the same or slightly better capacity, while a faster discharge (>1C) generally produces more heat and thus reduces the capacity, sometimes significantly.

Related Pages

 * List of Battery Types
 * Primary cell