I have had nothing but problems with removeable battery grips, starting with the 20D and up to the 5s. Most times, it was oxidation on the contacts, other times, it was just odd. That was with both Canon and 3rd party grips.
Hence, why I got rid of all bodies that weren't 1-series, no more grip problems! I only have one "gripped" body left - 1VHs and it's been fine, oddly enough!