If it's of any relevance, LP-E4N batteries from a 1Dx are backward compatible in older LP-E4-enabled 1D cameras (1D3, 1D4, and 1Ds3), LP-E4 batteries work in a 1Dx (with albeit less capacity). Both batteries are compatible with both chargers (LC-E4 and LC-E4N), though there's a 10% capacity reduction in one or more combinations (can't remember which). I've had a couple of surprises where one of my LP-E4* batteries "woke up nearly dead" in one of my cameras, but I can't remember the exact combo and it has been infrequent (so not a trend).

