Most of the Canon cameras can be used on an external power supply.

The aim of this page is to help those who want to use a non-Canon PSU or an external battery power supply to run their cameras. This is essential for very long exposures, and for scripts that run continuously, monitoring a scene, for example, in a security camera or wildlife setting.

Please could people add in the pin polarity and voltages that their model of camera can run on.

Camera model	Pin polarity	Stated voltage	Peak current	Waiting		Half press		Full press		Zooming		Playback
				Monitor on	Monitor off	Monitor on	Monitor off	Monitor on	Monitor off	Monitor on	Monitor off
A560	Outer pin -ve	3.15V	720mA	360	70	450	340	500		530	210	150
A590	Outer pin -ve	3.15V
A720IS	Outer pin -ve	2.95-3.15V	920mA

To calculate the time a battery will last, take the capacity of the battery, then divide by the average current drawn.

For example: A monitoring application has the LCD on all the time, and is wired to a 1400mAH battery pack. Sitting in the half-press mode for almost all the time, this means the battery will last roughly 1400mAH/450mA = 3.1 hours. The same camera attached to a 12V SLA with 40AH capacity will last for roughly 40/.45 = 88.8 hours or 3.7 days. (Note that this ignores losses in the battery discharge and gains from voltage conversions.)