Why do some chargers bill per minute instead of per kWh?

Historically because in some states only a regulated utility could sell electricity by the kilowatt-hour, so networks sold time instead. Many states have since carved out an exemption for EV charging, and separately, stations built with federal NEVI money must display a price based on $/kWh under 23 CFR 680.116(a). Per-minute billing still survives on older equipment and at sites that took no federal funding. Check your own state through the DOE Alternative Fuels Data Center laws database.

Can the price go up in the middle of my charging session?

Not at a station built with federal highway money. 23 CFR 680.116(a)(2) requires the displayed price to be the real-time price and states that the price at the start of the session cannot change during the session. The rule reaches NEVI projects and other publicly accessible chargers funded under Title 23 (23 CFR 680.102), so it follows the funding rather than the network's logo — a station down the road built privately is not covered by it.

When does an idle fee start, and can I avoid it?

It starts after your session ends and you are still occupying the connector, usually after a grace period of a few minutes. The amount, the grace period, and whether the fee scales with how busy the site is are all set per network and often per station, so the only reliable place to read it is the charger screen or the station detail page in the app before you plug in. Electrify America's pricing page says exactly that: refer to the charger screen or the app for current idle fees.

Does a membership always save money on public charging?

No. A monthly fee only pays for itself above a break-even number of kWh, and that number depends on the discount rate and on how much of your charging happens on that one network. Stations built with NEVI funds also cannot require a membership to charge, and cannot slow you down for not having one, under 23 CFR 680.106(f).

EV Charging Cost per kWh: Session and Idle Fees

A charger screen shows a price and a start button. What it does not show, in any size you can read from the driver's seat, is which of four different things that price is counting.

Get the unit wrong and the arithmetic turns on you at the worst possible moment in the session. A station billing by the minute keeps the meter running at full rate through the last ten minutes, while the car has quietly stepped down from 150 kW to 22 kW because the pack is nearly full. Time billing charges you the most for the stretch where you receive the least.

So this is a decoder for what sits behind the number: the four things a station can bill you for, where each one is written down, and why the same network's screen can look different once you cross a state line.

Worth knowing before any of that: the machine is a commercial measuring device in the same sense a gasoline pump is. NIST Handbook 44 carries a Section 3.40, Electric Vehicle Fueling Systems, added as a tentative code in 2015 and switched to permanent status effective 1 January 2023, and it requires an EVSE used to charge vehicles to be "of the computing type" and to indicate the electrical energy, the unit price, and the total price of each transaction (2026 edition, read 18 August 2026). Handbook 44 is a model document, though. It reaches any particular charger only through whatever a state's weights-and-measures law has adopted, which is where the state line comes back in.

Four line items, and only one of them is electricity

Pull any DC fast charging receipt apart and it is some combination of these.

Line item	What it meters	Where the number is published
Energy price	$/kWh delivered to the battery	Charger screen before start; station detail in the network app
Time price	$/minute the session is active	Same place, sometimes split into tiers by power level
Session fee	A flat charge for connecting at all	Often only in the app's fee breakdown, not on the big screen
Idle or congestion fee	$/minute after charging ends and you stay plugged in	Charger screen and app; grace period stated separately

Two more can land on top. Sales tax, which some states apply to EV charging and some do not. And parking, which belongs to the property owner rather than the network, and which is the fee most likely to ambush you at a garage or a hotel.

The tiered time price is the one people misread most often. Some networks charge a different per-minute rate depending on the power level your car is accepting, so a car pulling 60 kW pays a lower per-minute tier than one pulling 150 kW. It sounds fair. It behaves strangely, because your car crosses tiers mid-session as the battery fills.

The state line changes the screen, not the network

Two forces set the billing unit, and they pull in opposite directions.

The old one is utility law. In a number of states, selling electricity by the kilowatt-hour was historically reserved to regulated utilities, which pushed charging networks to sell minutes rather than risk being classified as a utility themselves. Many states have since written an exemption for EV charging. Several have not, or have done it only partly. The DOE's Alternative Fuels Data Center laws database is where to check your own state — filter to Electricity and read the entries about public utility definitions. The state pages follow a fixed URL pattern, so California's electricity laws page becomes ?state=TX or ?state=NY by editing two letters.

The newer force pushes the other way, and it comes from an unexpected place: weights and measures law, the same body of rules that governs a supermarket scale and a gasoline pump. California is the clearest case. Under the state's EVSE regulation, a charger that dispenses electricity as retail motor vehicle fuel for a fee is treated as a commercial measuring device, subject to county inspection like any other device that sells by measure. The California Division of Measurement Standards ZEV page (read 2026-08-18) lays out the phase-in: new commercial AC chargers installed on or after January 1, 2021 are fully subject, new DC fast chargers on or after January 1, 2023, while AC units installed before 2021 have until January 1, 2031 and older DC units until January 1, 2033.

One physical detail from that FAQ is worth carrying with you. Compliant units carry a county approval seal, which the department describes as indicating the unit has been inspected, tested and determined to comply with the regulation. Older units, still legal until their deadline, may carry no seal and may not yet meet the labeling and marking requirements. Next time you are standing at a California charger, look for the sticker.

The handbook settles the unit question in one line: EVSE units "shall be indicated and recorded in kilowatt-hours (kWh) and decimal subdivisions thereof," language amended into Section 3.40 in 2022. It also asks for something you can check from where you are standing. S.2.4.2 requires the machine to indicate conspicuously, on each face, the maximum rate of energy transfer and the type of current tied to each unit price — the handbook's own examples are "7 kW AC, 25 kW DC." A price quoted with no power figure and no AC-or-DC beside it is not showing what that code asks for.

Per-minute pricing bills your charging curve

Here is what makes time-based pricing expensive in a way that has nothing to do with the posted rate. The numbers below are invented, to show the shape. They are not anyone's current price.

Say a station charges $0.35 per minute, and your car takes 30 kWh in 25 minutes going from 10 to 60 percent. That is about $0.29 per kWh. Half a pack in 30 kWh puts this car near 60 kWh usable, so run the same car from 60 to 90 percent and you are asking for roughly 18 kWh — except it has tapered to 30 kW by now, so those 18 kWh take about 36 minutes. The same $0.35 per minute lands at about $0.70 per kWh, more than twice as much for identical electricity.

Nothing about the station changed. Your battery's acceptance rate did.

Three things move that curve, and every one of them lives on your side of the connector. State of charge is the big one, because every pack tapers as it fills: the top 20 percent is the slowest stretch, which under per-minute billing makes it the most expensive electricity you will ever buy. Temperature does the same damage for a different reason. A cold pack accepts less, sometimes far less, until it warms, so winter can turn a time-billed session into a bad deal before you have done anything wrong.

The third one is fixed before you ever pull in — the car's own ceiling. A vehicle that peaks at 77 kW pays the same clock as one that peaks at 250 kW. That is the DC-side cousin of the AC limit in 40A vs 48A vs 80A: different hardware, same lesson, the car rather than the equipment usually setting the rate.

Degradation nudges this too, though less than forum threads suggest. If you want to know where your own pack sits, reading state of health covers the screens that report it.

The practical rule falls out on its own. At a per-minute station, charge to what gets you to the next stop and go. At a per-kWh station the incentive flips: the slow tail costs the same per kWh as the fast opening, so stay if the stop is a pleasant one.

What federal funding forces onto the screen

Stations built with National Electric Vehicle Infrastructure money carry obligations that privately funded stations do not, and they are worth knowing because they are specific and written down. The rules sit in 23 CFR Part 680, pulled here through the eCFR on 2026-08-18 against the Title 23 issue dated 2026-08-14.

Read § 680.102 first, because the reach is wider than the NEVI label suggests: the part applies to NEVI Formula Program projects as well as projects building publicly accessible EV chargers with funds made available under Title 23 of the U.S. Code. Federal money, not the program's name, is what switches these duties on.

23 CFR 680.116(a) governs price communication:

The price must be displayed before you initiate the transaction, and must be based on the price for electricity in $/kWh.
The displayed price must be the real-time price, and — the sentence worth memorizing — "the price at the start of the session cannot change during the session."
Price structure "including any other fees in addition to the price for electricity to charge must be clearly displayed and explained."

That last clause is what you point at when a session fee turns up on a receipt and nowhere on the screen.

23 CFR 680.106(f) governs payment, and two of its four subsections are consumer protections most drivers do not know they hold at these stations: the station may not require a membership for use, and may not delay, limit, or curtail power flow on the basis of payment method or membership. It also requires a contactless payment method that accepts major debit and credit cards, plus a toll-free number or SMS option for starting a session.

The catch is still scope. These duties attach to the funding, not to the brand, and nothing on the pedestal announces which. Two stations from the same network can sit twenty miles apart with only one of them covered, and no consumer-facing badge distinguishes them. That is a real gap in a rule otherwise written for drivers. Your state DOT's NEVI award list is the closest thing to a paper trail if you need to settle it.

Idle fees are a parking meter with a very short grace period

An idle fee begins when your session ends and your car still occupies the connector. A congestion fee is a newer variant that can start while you are still charging, at busy sites, to discourage filling all the way to 100 percent.

Three variables decide what you pay, and all three vary by network and often by station: the rate per minute, the length of the grace period, and whether the fee scales with how full the site is. Do not memorize a number for any of them. Networks change them, and they change them per location. Electrify America's pricing page (read 2026-08-18) declines to publish a national rate at all: pricing is "determined by charger location, your plan, and the amount of energy delivered," idle fees "may be imposed for parking time after your charging session has ended," and the page tells you to refer to the charger screen or the app for current pricing, power levels and idle fees. Time-of-use pricing is live at select stations too, so the same charger can quote different numbers at 6 p.m. and at 11 p.m.

Which means the number you want is on the station detail screen in the app, before you drive there. Not on a comparison blog. Not on the network's homepage.

While you are in the app, switch on session-complete notifications. The idle fee is the one charge on this entire list that is fully inside your control, and it is lost in its entirety to a phone left on silent inside a shopping mall.

If one lands on you anyway, the receipt is where it gets argued. Handbook 44's UR.3.3 sets out what a receipt must carry, and time-based charges get their own subparagraph: any additional separate charge — parking time is the handbook's example — has to arrive with the time and date the service begins and ends, or the total interval purchased, plus the unit price applied and the total price for the time measured, on top of the energy quantity, the energy unit price, the EVSE identification number and the final total. An idle fee that shows up as a single unexplained dollar amount is missing most of that list.

The forty seconds before you press start

Standing at the connector, in order:

Read the unit. Per kWh or per minute? If per minute, pick your target state of charge right now, and make it lower than instinct suggests.
Look for a session fee and any minimum charge in the fee breakdown, not just the headline rate.
Note the idle rate and the grace period, then set a phone alarm for a few minutes before you expect to finish.
If the site uses time-of-use pricing, check whether waiting twenty minutes drops you into off-peak.
Photograph the screen. If the receipt disagrees with it later, that photo is your whole case, and at a NEVI-funded station 680.116(a)(2) is the rule you are citing.

None of this makes public charging cheap. Against an overnight rate at home it rarely will be, which is exactly why the home side of the question — whether your panel has room for a Level 2 circuit at all — deserves settling first, and NEC 220.87 lets you calculate that from your own utility bill.

The fast charger you use most has four numbers attached to it — billing unit, session fee, idle rate, grace period — and all four are sitting on its station detail page in the app right now, readable from a couch rather than from a windy forecourt. Copy them into a note with today's date beside them. The date is the part everyone skips, and it is the part that decides whether the note is still worth anything next spring.