What happens if you put the connector of a live charger in your mouth?
This is not the same as putting the terminals of a battery across your tongue. Modern wall warts/chargers are likely to have an open circuit voltage to earth (on both output conductors) of many tens (if not hundreds) of AC volts due to the way they are constructed. Normally this isn't a problem because the impedance behind this voltage is quite high.

I would expect that putting one or both terminals on your tongue would be slightly more shocking that the equivalent battery.

As a side note, this AC voltage is due to the way EMI filter components are used - at regular AC frequencies they are fairly high impedance (tens of kohm) but they will give a bigger than expected jolt on the tongue and this is not to be recommended.