Canon have released a newer version of LP-E6 which basically is the same format with minor internal changes which has to do with the new air travel regulations and some other international battery safety regulations. LP-E6N also have a slightly higher capacity than the older LP-E6 battery otherwise they are interchangable (except the charger!, read bellow).
Can I use the LP-E6 batteries in my new Canon camera which comes with an LP-E6N battery ? YES you can! However Canon says that you cannot charge an LP-E6 battery with the new charger for the LP-E6N battery.
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