Rapidly charging via 9V 1.8A charger

Hello! I've bought LG's MCS-H05EP travel adapter (like this one http://ift.tt/2bVG6Tu) which is sold with USB A to USB Type-C cable. On the adapter it is written 9V at 1.8A or 5V at 1.8A. The stock adapter goes for 5V at 3A which activates the rapid charging. So, I was quite surprised that the rapid charging also gets activated (and the device charges as fast as it does with the stock adapter) using the MCS-H05EP travel adapter. Here http://ift.tt/1HezzzM it is said that "The input voltage range between the wall outlet and this charger is AC 100V–240V, and the charger's output voltage is DC 5V, 3A." So, I'm kinda concerned whether the 9V@1.8A output from the custom adapter could damage the battery.
What you think, guys?

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