Tesla Motors upset some of its Model S owners this month with messages incorrectly singling them out as hoggers of the automaker's Supercharger electric charging network.

The Superchargers are extra-fast DC chargers, typically located along interstate highways, that work exclusively on Tesla vehicles, and that were designed to give road-tripping Tesla owners a spot to top up their battery. Tesla currently has 495 operational Supercharger stations worldwide.

But last month Tesla CEO Elon Musk explained the company had found several Superchargers, which had previously been advertised as "free forever," were being abused by local owners who happened to live nearby and didn't want to add to their own electricity bills by charging at home.

Last week, Tesla Motors sent out letters and emails to hundreds of owners it determined were taking advantage of the free electricity provided at their local Supercharger, asking them to consider charging at home more often and to cut back on their Supercharger use for the sake of long-distance travelers.

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“As a frequent user of local Superchargers, we ask that you decrease your local Supercharging and promptly move your Model S once charging is complete. Doing so ensures a better experience for the whole Tesla ownership community and allows Supercharger resources to be available for those who need them most.” Tesla said in the note.

The problem is the algorithm used to identify which Model S owners to send the messages to was, apparently, flawed: many recipients of the note lived nowhere near a Supercharger, and others who did used it sparingly or not at all.

Some owners who likely should have been sent the letter weren't, said writer David Noland of Green Car Reports, a self-identified local Supercharger "hog" in a post on the subject.

Other owners took offence to the tone and wording of the letter, which appeared to chastise them for the use of a utility the company had previously promised would be forever free and completely unlimited.

Tesla has not expanded on how many owners were sent the messages or replied to the negative feedback they've generated.