Engineers Edge

Capacity and Battery Ratings Review

Battery Application & Technology

Capacity and Battery Ratings Review

In general terms, the capacity of a cell/battery is the amount of charge available expressed in ampere-hours (Ah). An ampere is the unit of measurement used for electrical current and is defined as a coulomb of charge passing through an electrical conductor in one second. The capacity of a cell or battery is related to the quantity of active materials in it, and the amount of electrolyte and the surface area of the plates. The capacity of a battery/cell is measured by discharging at a constant current until it reaches its terminal voltage (usually about 1.75 volts). This is usually done at a constant temperature, under standard conditions of 25C (77F). The capacity is calculated by multiplying the discharge current value by the time required to reach terminal voltage.

The most common term used to describe a battery's ability to deliver current is its rated capacity. Manufacturers frequently specify the rated capacity of their batteries in ampere-hours at a specific discharge rate. For example, this means that a lead-acid battery rated for 200 Ah (for a 10-hour rate) will deliver 20 amperes of current for 10 hours under standard temperature conditions (25C or 77F). Alternatively, a discharge rate may be specified by its charge rate or C-rate, which is expressed as a multiple of the rated capacity of the cell or battery. For example, a battery may have a rating of 200 Ah at a C/10 discharge rate. The discharge rate is determined by the equation below:

Battery capacity varies with the discharge rate. The higher the discharge rate, the lower the cell capacity. Lower discharge rates result in higher capacity. Manufacturer's literature on batteries will normally specify several discharge rates (in amperes) along with the associated discharge time (in hours). The capacity of the battery for each of these various discharge rates can be calculated as discussed above.

The rated capacity for lead-acid batteries is usually specified at the 8-, 10-, or 20-hour rates (C/8, C/10, C/20). UPS batteries are rated at 8-hour capacities and telecommunications batteries are rated at 10-hour capacities.

Spider Optimizer

© Copyright 2000 - 2021, by Engineers Edge, LLC
All rights reserved
Disclaimer | Feedback
Advertising | Contact | Privacy Policy


Spider Optimizer

Register | Login

Engineering Book Store
Engineering Forum
Excel App. Downloads
Online Books & Manuals
Engineering News
Engineering Videos
Engineering Calculators
Engineering Toolbox
GD&T Training Geometric Dimensioning Tolerancing
DFM DFA Training
Training Online Engineering
Advertising Center

Copyright Notice

Publishing Program