Standby power draw
Standby power is what a charger consumes while plugged in but not charging — typically 1–8 W. At 5 W standby, a charger burns about 44 kWh a year doing nothing; the best certified units draw under 1 W.
ENERGY STAR’s EVSE dataset reports measured "no vehicle mode" input power for every certified charger, which is the number shown as standby draw on this site’s spec pages — a genuine differentiator between otherwise similar models.
| Range across the certified list | 0 W to about 15 W in no-vehicle mode |
|---|---|
| Median certified charger | About 3.5 W |
| Conversion | 1 W continuous = 8.76 kWh per year |
| Cost of 1 W | $1.49 per year at $0.17/kWh |
| Median unit’s annual cost | About $5; the highest certified unit, about $22 |
| Share of a typical charging bill | Under 1% of the ~$580 a 12,000-mile year costs at home |
Where the watts actually go
A wall charger is energised continuously, and the first thing it does with that energy is generate its control pilot. The 1 kHz ±12 V square wave runs whether or not a car is present, because that is how the charger detects a vehicle arriving — the car pulls the pilot from 12 V down to 9 V, and something has to be watching. That oscillator and its detection circuitry are the irreducible floor.
On top of that sit the contactor coil, the microcontroller, any Wi-Fi or cellular radio in receive mode, the LED ring or display backlight, and on commercial-style units an RFID field and card reader. ENERGY STAR prices each of these explicitly: roughly a watt for Wi-Fi or Ethernet, two for cellular, 1.5 for an RFID reader, five for a card reader.
The most interesting allowance is the one that scales with amperage. In Idle Mode — car connected, charging authorised, no current flowing — the criteria permit an extra 0.4 W per amp of rated output. An 80 A charger therefore gets far more headroom than a 32 A one, because holding an 80 A contactor closed genuinely takes more coil power. That is why bigger chargers legitimately idle higher, and why comparing an 80 A pedestal against a 32 A wall box on standby alone is not a fair fight.
The arithmetic, and where it lands
There are 8,760 hours in a year, so one watt of continuous draw is 8.76 kWh annually — about $1.49 at the US average residential rate of roughly $0.17/kWh. From there everything is multiplication: the median certified charger at 3.5 W costs about $5 a year, a 5 W unit about $7.50, and the highest-drawing certified model at around 15 W about $22. At California-style $0.30/kWh, multiply by about 1.8.
Put that against the charging itself. Twelve thousand miles a year at 3.5 mi/kWh is roughly 3,400 kWh, or about $580 at $0.17/kWh before charging losses. Standby at the median is under 1% of that. The entire spread between the best and worst certified charger is less than what you spend on electricity in a fortnight of normal driving.
So the correct weight to give this number is: tiebreaker. When two chargers match on amperage, installation type, cable length and enclosure rating, take the lower standby figure — it is free money and it is measured. What it must never do is override amperage fit. Buying a 32 A charger for an 11.5 kW car to save five watts trades roughly $7 a year for an hour and a half of extra charging time on every deep charge.
What you can and cannot do about it
The honest answer is that you choose it at purchase and then live with it. There is no user-serviceable way to lower a charger’s idle draw meaningfully. Some units let you dim or disable the LED ring or display, which is worth a watt or so on models with a bright screen. Disabling connectivity on a networked unit saves the radio’s watt, at the cost of the features you paid for.
Do not try to switch it off. A hardwired charger is not designed to be casually de-energised, and putting a plug-in charger on a consumer smart plug or timer is genuinely dangerous — those devices are not rated for 40 A continuous and the contacts will fail. Switching a charger’s circuit at the breaker daily is also poor practice; residential breakers are not rated as switches for routine operation.
Portable cord sets are the exception, and it shows in the data: several units report effectively 0 W because they fully de-energise when unplugged from the wall. If you keep a dual-input cord set as a travel or backup charger, unplugging it between uses genuinely takes its consumption to zero. For a mounted wall unit, choose the number on the spec page and stop thinking about it.
Frequently asked questions
How much electricity does an EV charger use when not charging?
Between effectively zero and about 15 watts, with a median around 3.5 W across ENERGY STAR certified models. At 3.5 W that is roughly 31 kWh a year, about $5 at $0.17/kWh. Networked units draw a little more than non-networked ones, and higher-amperage units are allowed more because their contactors take more power to hold closed.
Should I unplug my EV charger when I am not using it?
For a hardwired wall unit, no — it is not designed to be de-energised routinely, and the saving is a few dollars a year. For a portable cord set, sure: many drop to essentially zero when unplugged from the wall, and you were probably moving it anyway. Never put a Level 2 charger on a consumer smart plug or timer; those are not rated for continuous 40 A.
Do smart chargers use more standby power?
Yes, slightly. ENERGY STAR explicitly allows about one extra watt for a Wi-Fi or Ethernet radio and two for cellular, and the measured data reflects it — networked units idle higher than non-networked ones. The difference is a couple of dollars a year, which should not outweigh a utility rebate or a load-management feature you actually need.
How do I calculate standby cost per year?
Multiply watts by 8.76 to get kWh per year, then by your electricity rate. One watt is 8.76 kWh, about $1.49 at $0.17/kWh. So a 5 W charger costs 43.8 kWh, or roughly $7.45 a year; at $0.30/kWh it is about $13. Every ChargerAtlas spec page lists the model’s measured no-vehicle draw.