Let me know if this question is naively wide or not suitable for this site, I hope it's not because while I'm asking about manufactured devices, similar questions rise when designing a power source for a crafted devices.

Simply put, the question is: what powerbanks I can use to charge my laptop?

  1. Laptop params. The native charging device reads "output: 20V⎓3.25A 65.0W/15V⎓3A/9V⎓2A/5V⎓2A 10.0W", so it gives 20V*3.25A=65.0W. In specs, I've found:

    • Integrated Li-Polymer 57Wh battery, supports Rapid Charge (charge up to 80% in 1hr) with 65W AC adapter
    • native AC adapters (all USB-C, support PD 3.0, expect input 100-240V, 50-60Hz) give either 45 or 65W

    Is there something that I should look for in specs as well? It sounds like "the charging device output must have power of 45-65W; required voltage and current are unknown".

  2. Charging device. I have a powerbank that sais its output up to 15W, up to 2.4A at 5.1V, up to 1.2A at 12V. This is somewhat clear but why different power (2.4A * 5.1V ≠ 1.2A * 12V)? Is there a way to estimate what it will give at 10V (without measuring)? This question is important because a powerbank params can match device (laptop) params inaccurately.

  3. Params mismatch. Imagine that I see some charging devices on a market, and some of them have params different from 20V * 3.25A. Which ones can be used? Like, can I use those with the same power and voltage no less than target one? Or what if one has 20V and 3A: will it charge? May it charge? Can it hurt the battery? What about those with params greater than the required ones, like 25V*4A?

Presumably this is difficult to fully cover, but any widening of options compared to just "powerbank has to claim output of 20V*3.25A" and pointers to underlying principles are welcome. I had similar questions when trying to pick a battery for Raspberry Pi and Arduino projects.

  • 1
    \$\begingroup\$ These adapters are not battery chargers in electrical terms - they are constant-voltage power supplies, a.k.a. voltage sources. The actual charging circuitry is inside the laptop. \$\endgroup\$ Commented Jun 3, 2022 at 12:22
  • 1
    \$\begingroup\$ look up "USB-PD", eg here electronics.stackexchange.com/questions/372477/… The whole point of PD is that every device will do their best to work with any other device. \$\endgroup\$
    – Agent_L
    Commented Jun 3, 2022 at 12:41
  • \$\begingroup\$ @Agent_L thanks! That's something to start from. \$\endgroup\$
    – YakovL
    Commented Jun 3, 2022 at 14:09

1 Answer 1


Your question is off the rails a bit, because you want to know which USB powerbank can charge your laptop. This is akin to asking which one can run your dryer. They aren't big enough to do that job.

We see the same misconceptions in "solar generator" marketing, they say it will run your fridge, yeah for about 6 hours if you run nothing else. It's really deceptive and encourages magical thinking about battery capacity.

Battery capacity is in watt-hours

You seem to be familiar with a unit called the "watt" or (simpler) the "VA". I say that because you have figured out that [email protected] (10.71 VA) is not the same as 1.2A@12V (14.4 VA). These are units of power.

VA is basically the same unit as watts, and we need to switch because batteries are rated in watt-hours.

For instance a "car battery sized" deep cycle battery is 1000 watt-hours to max discharge depth (not a good idea with lead-acid). A refrigerator takes about 1000 watt-hours per day.

Most "power banks" have a rating that is fairly hidden, but stated as thousands of milliwatt-hours. "Milli" means 1/1000, so watch out! 18,000 miliwatt-hours sounds like a lot right? It is 18 watt-hours.

Onxe you have watt-hours, you cna divide by watts (VA) to get runtime. For instnace a 22,000 miliwatt-hour supply will run a 65 W laptop for ... 21 minutes.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.