Originally Posted by dave1993
toy chargers that are little more than a resistor and diode
Buy a V911 and open up the charger. You will find more than a resistor and diode.
Then you have USB voltage which is a regulated +5 volts. The battery charges to 4.2 volts - you are not going to cook a battery with that little voltage difference.
Inside the USB plug may be where they hid your resistor and diode.