What are peoples thoughts or experiences with using third party batteries for their Canon cameras? I like to have a spare battery just in case, (though I don't remember ever needing one!) but so far have always gone with the Canon branded ones. Here in the UK you can be looking at £70 to £80 for the more up to date versions though! This is starting to seem a bit excessive for a "just in case" item. I wouldn't want to take a chance if others have had negative experiences, and I'm just asking out of interest for the future really. Thanks. Paul.