NeOak
Member
Figured it was threadworthy due to the measurement and breakdown of the docked and undocked modes, as well as with a power bank:
Docked
Undocked
Battery Pack (USB)
http://www.anandtech.com/show/11181/a-look-at-nintendo-switch-power-consumption
Takeaway:
If you use a USB Power Bank/Battery that only does 5V, don't expect the Switch to charge the battery, since it will only pull 2A max even if the battery can give more.
If you want a USB Battery that can charge the switch, it needs to have USB PD:
https://www.ravpower.com/26800mah-Type-C-external-battery-charger-black.html
Amazon link: https://www.amazon.com/gp/product/B01LRQDAEI/?tag=neogaf0e-20
Docked
With the Switch charged and running Zelda in its docked configuration, it's drawing on average 11 Watts of power. The dock itself is consuming a bit of this energy to power its DisplayPort to HDMI converter, but it's safe to assume that virtually all of that power is going to the Switch itself. And while I didn't pull noise measurements on the Switch, while the console's fan was active, it was holding at a fairly low speed, judging from the softness of the sound.
Letting the Switch discharge and loading up Zelda again finds that power consumption has (unsurprisingly) increased, to 15.7W. Throwing on the partially discharged joy-cons bumps that up a bit further to 16.5W, coming fairly close to the official 18W limit of the dock. One thing to keep in mind here is that if we subtract out the 11W from earlier, we only end up with 4.7W left to charge the Switch's battery.
Finally, if we turn the console off and just let it charge, we find that the Switch + dock draws 9.8W. This is nearly twice the amount of leftover power the Switch had available to charge its battery with when it was docked and turned on. Meanwhile, adding the joy-cons to the mix to recharge as well brings the total power consumption up to 12.1W. The takeaway? The Switch can recharge fairly quickly, but only if it's not turned on. If it is on, it will still recharge in the dock, but at around half the rate.
Undocked
Starting off again with a fully-charged Switch, with the display at minimum brightness we're down to 7.1W, or 3.9W less than when it was docked. Considering that some of this power is going to screen and that we can't shut it off, we're easily looking at a 5W+ reduction in SoC power going from docked mode to undocked mode. Meanwhile cranking up the brightness to maximum increases the power consumption to 8.9W, or about 25%. In practical terms this means that going brighter definitely has an impact on the Switch's battery life, but even if you drop to minimum brightness, you're still only going to cut power consumption by 20%. So don't feel bad playing the console with a higher brightness; lowering the brightness won't vastly increase the runtime of the console.
Otherwise, keep in mind the 8.9W number. This is (roughly) the maximum power draw for gaming on the console when it's undocked. It should also be noted that the Switch will try to avoid charging the joy-cons unless it too is being charged, so the runtime impact of the joy-cons will typically be nil when the Switch is running on its internal battery.
After letting the Switch discharge, the power numbers for operating the Switch while it's turned on and charging are not all that different from earlier when the console was docked. With the brightness at maximum – to give us the Switch's maximum power draw undocked - the Switch draws 16.1W in this scenario. Throwing on the joy-cons adds another 1.6W, bringing the total to 17.7W. This is the single highest power draw number that I recorded, and it's interesting to note that it's still a hair under the 18W limit stamped on the Dock, indicating just how accurate that value is.
Finally, sleeping the Switch to let it charge is identical its power consumption while docked. The Switch will draw 9.8W to charge itself, and 12.1W with the joy-cons attached. Turning the Switch off entirely does change the charging rate a bit, but not significantly: it goes from 9.8W to 10.6W.
Battery Pack (USB)
Plugging the Switch into a power bank finds that a good power bank can provide enough power to run the Switch, but that's it. Whether discharged or full, the Switch doesn't pull more than about 9.1W from a battery pack. This is just over the 8.9W maximum operational power consumption level we established earlier. And even after letting the Switch run for a couple of hours off of a power bank and starting from a full charge, it's still fully charged while the power bank is slowly discharging.
Notably, the Switch can't draw more than the aforementioned 9.1W from the Xtron, or indeed any other tablet-sized power bank I've thrown at the Switch. In fact every 5V-capable USB-C power source I've thrown at the Switch maxes out at this same point. At 5V, the Switch doesn't seem to be able to draw more than 2 Amps.
The takeaway from all of this is that while this is by no means an exhaustive test, what I've found is that any good power bank designed to power tablets will be sufficient to power the Switch. So long as a bank can deliver 5V @ 2A or better, then it can power Nintendo's console. (And if you're looking for buying advice, while I haven't yet had a chance to test it, RAVPower recently started shipping a rather sizable 99 Whr power bank that supports up to 20V)
The one downside is that due to the inner-workings of the USB Power Delivery specification (more on that in a sec), the Switch apparently can't pull enough energy from standard 5V-output power banks to meaningfully recharge its battery while gaming. So with a 5V power bank, if your Switch is fully depleted, you'll need to stay attached to the bank the entire time you're playing, or take a break and let the bank recharge the Switch while it's sleeping. In the case of the latter, the recharge rate should only be a bit lower than if you had used the AC adapter.
http://www.anandtech.com/show/11181/a-look-at-nintendo-switch-power-consumption
Takeaway:
If you use a USB Power Bank/Battery that only does 5V, don't expect the Switch to charge the battery, since it will only pull 2A max even if the battery can give more.
If you want a USB Battery that can charge the switch, it needs to have USB PD:
https://www.ravpower.com/26800mah-Type-C-external-battery-charger-black.html
Amazon link: https://www.amazon.com/gp/product/B01LRQDAEI/?tag=neogaf0e-20
it seems like every decent USB-C power bank is 20000mah or more. I wish there was a 10000mah available. I don't really want to lug a 7x3x1ish bank around. :/