Charging 101
Charging speed depends on 4 factors: the capacity of your battery (in mAh), the output of your charger (in A), the charging speed of your phone (in A), and the usb charging cable you are using.
For example with Note 2. Stock battery is 3100 mAh (3.1Ah - charging capacity of 3.1A per hour), stock wall charger is 2A (it will supply 2A per hour at 5V which is standard usb interface voltage), Note 2 charging speed is 2A (it can take advantage of full 2A per hour charging speed), and stock usb cable is a thick cable with thicker power wires (creates less resistance so there is no loss at full charging speed).
So in ideal situation of you charging Note 2 with all stock equipment you will get 3.1Ah / 2A = 1.55 hours to charge battery from empty. Since external charger connects to the phone through usb port (5V) and the battery is actually 3.7V, there is internal conversion of voltage inside of the phone which results in additional losses due to efficiency. So even with 2A external charger (wall or car) you are getting more like 1.6-1.7A of current. So realistically we are talking about 3.1Ah / 1.6A ~ 2 hours of charging. This is IDEAL situation.
Now, if you are using a wall or a car charger that is rated at 0.7A - it will take even longer because you have about 20% loss due to usb port conversion and then you have to substitute 1.6A in the above equation with whatever 0.5A you have left. PLUS, if you are using a cheap or regular PC usb cable (those are intended for 500 mA current, pc usb port standard) - thin wires will create more loss. Or, if you have an extended 6200 mAh battery or 9300 mAh battery, you are changing numbers in equation again to make charging even longer.
Basically all these 4 factors will affect the charging speed. Also, keep in mind, if for example you are using 2A wall charger but your phone can only charger at 1A rate - your device will NOT draw more than 1A per hour from the charger. But if you are using 2A device with 0.7A charger, you only be drawing 0.7A per hour to charger your device.
Last but not least, someone made an app for Samsung phones which tells you the average current you are drawing during charging:
Galaxy Charging Current . Only works with Samsung phones and perfect for our Note 2!!!