Figuring out exactly how much it costs to charge Tesla Model S

Is the Tesla Model S an electricity guzzler? One driver trying to answer that question says it does gobble down more juice than previously thought, but it's not time to make Hummer jokes just yet.

First, the goal: Tesla's claims that properly set up home-charging stations can get about a 91-percent efficiency rate.

Rob M. from Teslarati has been diligently tracking electricity used by his home charging station – made up of a NEMA 14-50 outlet that was professionally installed and Tesla's Universal Mobile Connector (UMC) – since June, as we reported here. The results for the month that ended July 21 revealed that the Model S was taking in about 82 percent of the electricity it was pulling from the system, indicating an 18-percent loss of electricity. Most EVs are thought to charge at an 88 to 90-percent efficiency rate.

The downside to his results? About $26 more per month in electricity costs than previously estimated on about 2,400 miles worth of driving. There is a positive upshot, though: his monthly fuel savings totaled about $334 compared to driving an internal combustion engine vehicle.

These early results are intriguing, and make us wonder... Is anyone else checking in on their Model S charging efficiency?