It depends on the ecig, but the charger for it (or internal if USB charging) will typically charge at something less than 1 Amp. This is the constant current phase. So on a single cell if the voltage required for the cell to take 0.666Amps is less than the max cell voltage of 4.2V then it will current limit by holding the voltage back.
When the cell hits 4.2V to sustain the 0.666Amps then the current will start to fall back and 4.2V will be held. Eventually the current will drop off towards zero when it will end the charge.
As to "pass through vaping", ie. using it while charging, some will just pull from the cell while it's charging, so if you consume more than the charge current of 0.666amps it will go back into charge mode briefly to replace the current you used.