Awatere: This is happening to me, and my battery's serial number was manufactured in China and within the given range. I'm actually really pleased to finally understand why my S4 is doing this!
I've just ordered a replacement battery from TradeMe (I really don't want to be without my phone while it jaunts off to Telegistics).
Was the answer around safety ever discovered? This device and I are practically joined at the hip - is it safe to keep using it until the new one arrives, or should I dig one of my old phones out of the emergency drawer in the interim?
If yours is a Telecom sourced one call your local Telecom store as they may have one on hand to swap it with.