Got a big (as in 'never to be repeated') holiday coming up in a couple of months time. I'm considering taking a second battery with me in case - for whatever reason - my main battery or charger (as supplied with the camera when bought new) fail. I use a Canon EOS 70d & Canon's own batteries are not as cheap as generic alternatives. If I do buy a generic battery am I throwing good money after bad or are they (especially as I will only be buying a reserve that, hopefully, I will never use) reasonable value for money?