What's the best MFi certified Iphone 5 battery extender case?

I am looking for the best durable and best battery extender with an mfi certification.
Update: This is kind of strange but what's the point of MFi certification? LIke Maxboost doesn't have it. Does it matter?
Update 2: What is the best battery extender case you have found that incorporates everything like syncing, and reception?
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