How Accurate Are Powerbank Percentages?

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  Hybroid on 15/02/2021 - 10:26

  +1

  This has not been my experience with Anker powerbanks. You indeed lose some efficiency, so don't expect full mAh capacity, but that's quite a drastic difference. I would return it for a new one.

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  foxmulder on 15/02/2021 - 10:49

  Try another test. Make sure the power bank is completely empty thus won't charge your device. Then recharge powerball overnight till full then see how many times it recharges your device. Assume a 4000mah device it should do 6 times recharges. If not then it's faulty.

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  skid on 15/02/2021 - 11:08

  It's normal. The 100% -> 75% -> 50% -> 0% is on some sorta exponential scale. As in the drop from 100% to 75% takes longer than it does from 75% to 50%.

  Secondly, the 26800mAh is based on nominal voltage. Quora has a good explanation:

  The mAh rating given to a power bank is usually the fitted cell capacity at the nominal voltage, in the case of a power bank and lithium ion cells this is 3.7V. To understand how much power you can get from your power bank several things need to be understood. To start with the stated mAh rating is no use to you seeing as you will be using 5.1V (typically) from the banks USB outlet. To translate available capacity/power we need to convert mAh to mWh (milli Watt hours) or just Wh, this is just to use a common power figure. A 10,000 mAh 3.7V bank of cells will supply a theoretical 37,000 mWh (mAh x 3.7V). Lets convert that to what you will get at 5.1V (37,000/5.1V) and you now have ~7,255 mAh at 5.1V. Now take the inefficiency of the boost converter into account, they are typically about 90% efficient, and you now will get around 6528.5 usable mAh (at 5.1V) from a power bank marketed as 10,000mAh. You also need to account for losses in the charging circuit of the phone battery and the fact that the phone battery will itself have less than 100% charge efficiency as there are losses withing the battery as well. Ever noticed how your phone can feel a little warm when on charge? That’s some of the losses given off as heat. So a phone with a 2,600 mAh battery (cell) will likely only be able to be fully charged twice from a so called 10,000 mAh power bank.

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  aoeueoa on 15/02/2021 - 11:15

  It's working as normal but the issue is the charge current + voltage which depends on what you're charging. The later model phones take advantage of the higher current charging = faster = loss in efficiency and heat. It's the sacrifice you make for time. Faster charging on yours is up to 18watts (12v x 1.5a). If you were charging at a much lower current, you'd get much more of the capacity utilised. You can't change this though, it's up to the device to take what it wants from your powerbank.

  An old review of the xiaomi 10 000 banks here shows that at a low current you get 70% capacity delivered, and at high current you only get 30% delivered. Huge difference. The romoss is a different model but the same principles apply.

  https://budgetlightforum.com/node/55027

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  Mechz on 15/02/2021 - 11:20

  Hmm. I have the 30k Romoss and it does at least a week of charging for my phone and a couple extra charges for the wife. There's only an LED indicator and it's consistent down and up.

  I'm guessing yours has a bad cell or something.

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  BewareOfThe Dog on 15/02/2021 - 11:33

  +1

  "It goes from 100% to about 75% fairly normally - and then it drastically drops to zero."
  Sounds like my old AU Falcon station wagon's fuel tank. ;)

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  jonathonsunshine on 15/03/2022 - 09:39

  I bought a brand new romoss SW20 PS+ https://www.amazon.com.au/gp/product/B07WWV4T47/

  I charged it up to 100 from 75, used it to charge various things, last night it was at 15%, plugged my phone in and it only charged it 10% before hitting 0, and this happened very quickly.

  So I plugged it into my QC phone charger and it went very slowly to 1%, I rolled over in bed, a little bit later I rolled over and now it was on 17%. This can't have been more than 10 minutes later max.

  Did I get dud?