Battery life on one review was 220 pictures and on another it is 225 pictures. If you can afford it I would recommend getting a second battery.
Regarding ISO, the higher the number the more sensitive it is to light. For example, on a bright sunny day you would use a lower ISO setting vs a higher ISO setting on a dark or cloudy day. You would use a higher ISO to compensate for low light situations. Use caution when using a higher ISO setting as it will increase the amount of "noise" when shooting. I would experiment with the various settings to gain a better understanding of how they affect the shot.
http://digital-photography-school.com/iso-settings
http://www.photographymad.com/pages/view/what-is-iso-speed-setting
A more detailed explanation of ISO:
http://en.wikipedia.org/wiki/Film_speed
The ISO setting is often used in conjunction with the aperture setting. For example, on a bright sunny day you would use a lower ISO setting and a higher f/stop setting vs a dark or cloudy day where you would use a higher ISO setting and a lower f/stop setting. The aperture setting determines how much light is let in during exposure. In reality you would use a combination of the ISO setting, aperture (f/stop) and shutter speed.
Aperture explained:
http://en.wikipedia.org/wiki/Aperture
I hope I have not confused you with all of this.