Aside from the sleek and sexy design, Autopilot features, and speed, another come-on for Tesla electric cars are the free charging available at its Supercharger stations. However, that could change soon as Tesla announced that charging will soon incur some fees.

Come January 1 and Tesla will begin to charge a "small fee" to Tesla owners. Tesla assured, however, that the cost will still be lower than buying gas and there will still be free mileage. But instead of being free for life, Tesla will just give its car owners a 400-kWh of free Supercharging every year, which is equals to 1,000 miles of driving. The new rule applies to those who have bought Tesla after the rule gets implemented.

According to Tesla, the move to charge an extra fee is the company's expansion. The company says it is going to add more Superchargers to the existing 734 around the world. However, observers say that the fee might not just because of expansion. They say that a lot of Tesla owners are abusing the free lunch and treated it like a big buffet where a long line of Tesla cars line up to get their fix. Tesla was aware of this and issued a letter in 2015 chiding Model S and X owners not to abuse the service but instead do the charging at home.

According to Paul Mutolo, an energy storage chemist at Cornell University, one active Supercharger is equals to lighting 5 to 10 home simultaneously. Moreover, a number of cars charging simultaneously could create a sudden surge in power demands leading to overblown electricity bills.

Free charging will be more of a headache in the coming years as Elon Musk transitions from being a luxury car maker to a mass car manufacturer. This year alone, his company has sold 100,000 units and he vows to sell half a million more by 2020.