I just received my MBX today. I have this portable charger from anker which isn't able to charge it. But I just ordered this charger from Charmast hopefully it's able to charge it. I'm thinking it will since it's the updated version of the Charmast battery as the previous one was capable of charging the Macbook but not Macbook Pro, and this one can. I'll let you know if it is able to charge the MBX too.

Anker makes some great chargers, can't go wrong with one of those.

Depending on how much you're willing to spend, this one will charge your phone about 3-4 times and cost less than $25 while this one is $70 but will keep you charged all weekend.