# QuestionWant to learn about laptop powerbanks?

#### terryvalencia

##### Commendable
My laptop is dell inspiron 15 5567. I guess it's 65W laptop battery. It's 42000mWh battery. So, tell me if I buy 30000mAh powerbank, how many charges can it give to my laptop?
Also recommend best budget powerbanks under 50\$.

#### kerberos_20

##### Champion
hmm lets see
you laptop battery runs at 11.4v and got 42Wh (watt hour)
powerbank battery 3.7v 30AH = 111Wh (watt hour)
now theres also some power lost once you convert internal 3.7 from powerbank into whatever your laptop takes (20V?)..so lets assume youll get about 80% from your powerbank
so 111 * 0.8 = 88.8WH
that is for 3.7v, but you gonna need 11.4v , so youll end up with 29.6Wh

(29,6/42), the answer is simple, it will charge 0.7x (70%) your laptop battery

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#### kerberos_20

##### Champion
here is example of some random laptop charger powerbank, it can do two laptop charges, but its outside of your budget and its big, but it has to be bigger than your laptop battery to do more than one charge

#### hotaru.hino

##### Illustrious
Note, a watt-hour is a watt-hour. The laptop's battery capacity is 42 W-hr, while the example power bank's would most likely be 111 W-hr. Assuming we're charging at a rate of 1C (so laptop's capacity in one hour), we basically need to drive 42W into the laptop battery.

42W out of the power bank would be 11.34A at 3.7V, though that amperage is worryingly high (to put in perspective, the maximum coming out of your typical home outlet is around 12-15A). Also you need to boost the voltage up anyway because batteries need to be charged at a slightly higher voltage than it outputs. So for simplicity's sake, let's say the battery needs 14V to charge. That drops it down to 3A. Much more doable. And if it were generating an AC output, that drops it down further to less than half an amp.

This is all under ideal scenarios obviously.

In any case, you'd be able to charge the laptop around 2 times since the power brick isn't just charging the laptop.

#### hotaru.hino

##### Illustrious
So, if I want to charge my laptop 100% once, how much big power bank should I buy? I am from Nepal
https://www.daraz.com.np/catalog/?q...t&spm=a2a0e.11779170.search.go.287d2d2beprFOy
And these are the powerbanks available for me. Which one should I buy? All of them are from trashy companies.
So the thing is you can't simply plug in any battery bank into your laptop and expect the battery bank to charge. You have to find a battery bank that supports roughly the same output as the charger of the laptop, which should be a USB-PD standard profile if the laptop's only way of charging is via USB-C. If your laptop can be powered secondarily through USB-C, you'll have to refer to the manual for what input it needs.

After that, you find a battery bank that supports that outputs the same voltage and at least the same current. The more current the battery bank can provide the better, though mostly because it won't work the battery bank as hard. It won't charge the laptop any faster. So if your laptop requires say 3.5A at 20V, the power bank has to provide 20V and at least 3.5A, but a higher amperage (the A) is fine. You just don't want lower amperage.

Once you get to this point, then if you want at least one full charge for your laptop, you need something that provides the a little over the WHr rating of the laptop's battery. Remember: a watt-hour is a watt-hour. 3V at 5A for one hour is 15W-Hr, same with 15V at 1A for one hour.

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