Video camera battery life tip: Check the battery’s mAh (milliamp hour) rating. It's usually printed on a label on the battery itself, the battery company's website, or in the product manual. The higher the rating, the more charge the battery can hold. A rating of 7 mAH will give you about 7 hours of camera use.
To extend the life of your battery while shooting, use the viewfinder instead of the LCD screen, or, if you prefer not to use the viewfinder, remember to close the LCD screen when not in use. If you’ll be shooting for a long time, consider buying an extended-life battery. These larger,batteries cost more but can double a video camera’s battery life. Also, consider buying extra batteries to have as back-ups.