That is probably one of the most misguided and unclear things I've read about electricity in a long time. AC doesn't need any stronger conductors than DC, if anything it's the opposite...

Both DC and AC need two conductors. The powergrid is grounded to the earth, so anything with a low resistance path to ground can serve as one conductor.

As for danger, it's all about current through your body, and that depends on the voltage. For a given voltage, AC is probably more dangerous. The battery's 3 - 4.2V poses no electrocution danger.

The danger in the above case of the battery is not that you'd electrocute yourself, the danger is when using uninsulated wires that you'll accidentally let them touch eachother, which will lead to a short circuit, which can make the battery explode.

As for dapenzerg the lower voltage of 5.2V (compared to Nokia chargers' 6V or so) and the lower current of 500mA is probably what helped. The reason it reboots with a crap battery is that the hardware can't regulate the charge current low enough, which results in overvoltage on the battery. which makes the charger software abort, which makes dsme reboot the device.