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What the ENERGY STAR test measures on a charger

By Ethan WalkerPublished October 27, 2026Data as of October 27, 2026

ENERGY STAR measures a charger's input power with no car connected, with a car connected but not charging, and in a third partial-on state, and it sets an allowance for each listing's feature set. The median Level 2 listing uses 64.65 % of its standby allowance. Charging speed is not part of the test.

Three low-power readings

The ENERGY STAR test for AC chargers records input power in watts in three states where no charging is under way. No-vehicle mode is the charger powered with nothing plugged in; this site calls it standby draw. Idle mode is a car connected but not charging. The third reading is labelled partial-on in the data. Each listing on this site shows all three in its listing record.

Across the 424 Level 2 listings, the median standby draw is 3.66 W and the median idle draw is 6.175 W. Idle draw is higher than standby draw on 414 of them. The partial-on reading is within 10 % of the standby reading on 369.

The allowance

For no-vehicle and idle mode, every listing also carries an allowance: the most it may draw in that state for its set of features. The allowance is not one number for all chargers. On the Level 2 listings the most common standby allowances are 6.5 W (54 listings), 3.6 W (51 listings), 5 W (44 listings) and 7.5 W (22 listings). Listings with a high-resolution display have a median standby allowance of 8.605 W, against 6 W for the rest.

This site divides each listing's standby draw by its own standby allowance and calls the result allowance used. The median Level 2 listing uses 64.65 %. 31 use less than 30 %, and 51 use more than 90 %. 1 sit at or within rounding of 100 %. No listing is above its allowance; a certified charger cannot be.

Across all Level 2 listings the standby allowance itself runs from 2.6 W to 20.82 W. Of the ten listings with the largest allowances, 9 list a high-resolution display and 8 a credit-card reader. A plain ranking by watts and a ranking by allowance used can therefore place one listing very differently.

Allowance used and standby draw answer different questions. Standby draw is the plain number of watts. Allowance used says how close a charger sits to its own limit, given its features. A charger with a display and a cellular modem can draw more watts than a plain unit and still use a smaller share of its allowance.

The idle allowance

Idle mode has its own allowance, and it is much larger than the standby one: the median Level 2 idle allowance is 26.1 W. Measured against it, the median listing's idle draw uses 22.2 %, and only 22 of the 424 use more than half. This site therefore ranks the standby allowance share, where the listings are spread much more widely, and shows the idle allowance in each listing record.

The partial-on reading is above the standby reading on 309 of the 424 Level 2 listings; its median is 3.82 W. The data gives no allowance for it.

Reported loss while charging

The listing also reports the power lost inside the charger during charging tests at several currents. These values have no ENERGY STAR limit. 436 of the 461 listings carry a usable full-current value after the checks described on how to read the data. Of those, 103 are under 0.3 % while the main group sits near 1 %, a split that suggests different measurement practice between labs. For that reason this site shows the loss values on charger pages as reported figures and never ranks them.

Specification versions and dates

The source metadata lists three versions of the ENERGY STAR requirements for chargers: Version 1.0, effective December 27, 2016; Version 1.1, March 31, 2021; and Version 1.2, June 20, 2023. Certified models meet one of these. The certification dates on the current list run as below.

Listings certified in 2024 and 2025 make up 249 of the 461, and 26 date from before 2022.

Because the list changes as models are added or withdrawn, every rank and count on this site says “on the ENERGY STAR list” and carries the date of the data, October 27, 2026. Ranks are given within rating groups so that a 32 A wall unit is not ranked against an 80 A unit with two outputs.

None of these readings measure charging speed, which is set by the rating and the car. They describe what a charger draws when it is not charging, which is most of the time. The standby guide and the rating pages show the values for every listing.