Tesla's high-speed Supercharger network, and the effect it has in countering range anxiety, has had a lot to do with the company's success in the electric vehicle marketplace. Who doesn't appreciate free power-ups in a fraction of the time it takes other EVs? For early adopters, the deal was even sweeter: plenty of plugs and few fellow Model Ses to share with.

But these days there are many more Teslas on the road. Model S production has been flat-out for the past couple of years, and, despite teething troubles, Model Xes are also becoming thicker on the ground.

In EV-dense areas like Southern California, this has meant congestion at some Superchargers, and that in turn has led to frustration among customers who turn up needing juice only to find all the Supercharger spots being hogged by fully charged vehicles. Tesla says things have to change, so it has introduced an idle fee: block a Supercharger port with your fully charged Tesla from now on and you'll be charged $0.40 a minute (£0.30 in the UK, €0.35 in the eurozone).

Tesla says it plans to double the number of Superchargers by the end of 2017 and also plans to increase the number of "destination chargers"—that is, lower-speed chargers at hotels, restaurants, and shopping locations (we've even spotted them at a number of race tracks this year). But when Model 3 orders start being filled in volume, Supercharger ports will become a much scarcer resource that needs to be managed differently.

There will be no free Supercharger access at all for Model 3 owners. At the time of that last announcement, Musk reminded us that "the best thing to do with an electric car is to charge your car where you charge your phone."

Last month we learned that Teslas ordered after January 1 will only get 400kWh of free Supercharger access each year (as opposed to the "all you can eat" model enjoyed currently). This latest incentive to free up Superchargers is the next logical step—one that aims to change the behavior of existing customers who may have gotten into the habit of treating the high-speed network as just an extension of their garage.

All Model S and Model X EVs will be liable for idle fees. The fees will kick in after the vehicle's battery is full, although if the vehicle leaves the bay within five minutes the fee is waived. Owners will be charged at their next service center visit, and there is no upper limit on that charge (which works out at $24/hour). The fee is in effect right now, but Tesla has already modified the policy slightly: although the company had stated that idle fees will apply even if there are empty Supercharger spots available, Musk told Twitter that wouldn't be the case:

@TeslaMotors We are going to modify this so that people only pay a fee if most bays are occupied. If the site is basically deserted, no problem to park. — Elon Musk (@elonmusk) December 17, 2016

Tesla expects this problem to be a short-lived one, envisioning a future where the "cars move themselves once fully charged." But until then, you probably ought to set an alarm next time you head to the Supercharger (something Tesla's app will do for you).