UPDATE: There was a question, following our report, about which Nintendo Switch model we used to get our results. It was an important question. We used the original launch model to get our results, but there are another two versions of Switch hardware out there: the revised 2019 model and the newer OLED model. And these significantly alter the test results; power-use has been as much as halved in the newer models.
We decided, then, to re-test all three Switch models to produce a supplementary table to the original one below. On it, you will notice a discrepancy with the original Switch figures in the "Rest mode" category. We originally told you the launch model Switch would pull 3.5W in Rest mode, and that would add up to £10.40 of electricity used a year, but that is not entirely correct.
The complication comes from Switch being the only console that charges a battery. When it's charging, it does pull 3.5W, but when it's not, it pulls hardly anything: 0.2W the majority of the time. This reduces the annual pull to £0.59 - a trace amount.