Electronic cigarettes that look like the real thing and but don't contain tobacco are gaining steam despite calls for a ban of the battery-powered devices.

E-cigarettes are plastic and metal devices that heat a liquid nicotine solution in a disposable cartridge, creating vapor that users inhale.

Unlike other nicotine replacements, e-cigarettes have become the flashpoint for a legal fight over how risky they are compared with traditional smokes, if they're even legal, and if they are safe to use.

The Food and Drug Administration and public health groups have sounded the alarm on e-cigs, saying they contain dangerous chemicals and are being marketed to children. The federal agency had even halted shipments and several states have attempted to ban them.