Battery Capacity
Batteries run down under use. Their capacity is specified in ampere-hours
(Ah). The ampere-hour rating of a battery is equal to the product of its current
drain times the length of time that you can expect to draw the specified
current before the battery becomes unusable. For example, a battery rated at
200 Ah can theoretically supply 20 A for 10 h, or 5 A for 40 h, etc. The relationship
between capacity, life, and current drain is