I know that fast charge technology allow chargers to communicate with the battery management chip inside the mobile phone in order to use different voltages to charge the mobile phone instead of just using 5V and have a high current like 2A or 3A.
But I don't know how that charge is transfer inside the mobile phone to the battery. I know normally batteries are 3.7V.
How a fast charge using the same power (2A x 5V vs 1.11A x 9V) will affect the heat in the battery of the mobile phone ? I know that 2A will produce more heat in the wire/components, but not sure how it will affect the battery.
EDIT: I think the right answer is in another topic here.
Li-ion cell charging voltage ranges from ~3.7V to 4.2V. 18W/4.2V = 4.29A. The charger has a DC/DC voltage converter circuit which pulses current through an inductor to 'transform' the voltage down and current up. This process is typically 85~90% efficient, so it should be able to deliver 4A for most of the charge cycle.
So the heat will be the same, since its convert 9V voltage to 4.2V or 4.4V and increase current, no matter the method you use for fast charge.