How is the battery life on the Nikon D3100?

^^^^^^^^^
I'm thinking about getting it!

I own a D5100 and the battery lasts about 800-ish shots. I doubt the D3100 probably is any different. But that depends greatly on 1) whether or not you're using AF and VR 2) Temperature 3) Live view on/off etc etc. Regardless of what camera you end up getting, buy a spare battery or two.

That depends on how you use it. Video eats battery power for lunch. Still shooting you should be able to get about 500 stills per charge. Do you turn it off when you're not shooting? Uploading also consumes battery power and using a usb card reader is an efficient way of moving photos from your memory card to your computer.

I also recommend a minimum of three batteries in your bag. I carry two dslr cameras and no less than 6-batteries and 6 memory cards all the time. Then use each battery until it's done for that charge.

Never use your memory card for storage / display - cards love to fail when used this way.
Work flow: Shoot, upload, format in the camera - all the time, every time.

Well it's a standard, around 500 to 600 shots before getting empty. You shouldn't really worry about it as an extra battery can be bought for ~$40. The D3100 is a great camera that will allow you to shoot anything, as long as you know what you're doing.

Here's a DSLR Buying Guide - http://www.the-dslr-photographer.com/2009/11/which-dslr-to-buy/

Pretty darn good.
See page 204 in the instruction manual which you can download from Nikon.

The CIPA rating is 550 shots. This is a standardized test which also includes using the flash.

Nikon states you can get 2000 shots if you don't use flash, live view, and VR for a fairly realistic set of circumstances.

By the way, you don't need to turn off the power. The camera will draw the same amount of power when the power switch is in the off position or on position when the camera electronics goes to sleep. All DSLRs are like this.

To get better battery life, minimize the use of the LCD display.e. G., don't use live view and don't view your shots incessantly.

On my D40, I often will go on 1 week trips and not worry about bringing a charger since I usually won't take more than 1000 shots.