Should have been included with the portable battery charging pack,
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This review is from: Samsung ETA-U90UWE 5.1 V 2.1 A Travel Adapter Charger (Accessory)
I had to get this 2Amp charger for my portable battery charging pack. Without it, the charging took at least double the time. As I said above, this charger should actually be included when you buy the portable charging pack. It's pointless getting the pack and then having to wait ages for it to charge on a normal charger, or even longer via USB.
So don't think twice, when you buy the charging pack: Just get this charger as well.