Battery

Basics

Many electronic devices run off batteries as their energy source. The ideal battery is a source of voltage, when connections are made to it current will flow, the amount depending on the connections. For the ideal battery the voltage will not fall when current is drawn, or time goes by. For real batteries none of this is true, but may be useful approximations. An improved model of a battery is that it is an ideal voltage source in series with an ideal resistor ( known as the internal resistance of the battery ).

Some of the most imporatant characteristics of batteries:

• Voltage
• Internal Resistance
• Energy content ( often indirectly measured by amp hours )
• Primary ( not recaragable ) Secondary ( rechargable )
• Size
• Weight
• Chemistry ( lead-acid ...... )

Uses

• Provides power to circuits. At any time the power is equal to the voltage of the battery times the current. When the battery is not connected, the current and the power are 0.
• We will often use a power supply in place of a battery.

There are a surprising number of myths and urban legends about batteries (such as the "memory effect" near-myth and various ways of "fixing" it). Also the process of charging them up.

Further Reading

• "Performance Measurements of Some NiMH Battery Chargers" by Matt Blaze
• "The Great Battery Shootout" by Dave Etchells
• Wikipedia: Battery (electricity)
• Wikipedia: memory effect
• sci.electronics FAQ: NiCd Batteries do NOT have "memory"
• "Digital Photo Myths Dispelled" by Dave Johnson
• "Dan's Quick Guide to Memory Effect, You Idiots"
• Battery University
• "Charging NiMH Cells" mentions that "If the charge current is 1/40th the ampHr rating of the cell (c/40), ... pressure will not build up. The cell can be kept in a state of trickle charge for a long period of time without damage."