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I have a Dell laptop with these battery specifications from HWID HWMONITOR enter image description here

I want to buy a powerbank, and saw there are many 20k mAh/30k mAh batteries, as described by sellers. How can I check how many times the 20k/30k power bank can charge my device from 0 to 100% or 0 to 80% before the power bank empties?

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  • I am not sure if measuring battery capacity is a computer question under SU guidelines
    – John
    Jan 31, 2023 at 20:14
  • You have to know what's the voltage of the powerbank batteries to roughly estimate this.
    – gronostaj
    Jan 31, 2023 at 21:09
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    By trying it. Absolutely no other way. There's too many variables, power doesn't just "magically" go from battery A to battery B.
    – Daniel B
    Jan 31, 2023 at 21:10

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If the vendor is honest, it's not too difficult to calculate.

  • The computer has a "39994 mWh" battery, that is, about 40 W-h (i.e., can supply ~40 watts for 1 hour). A full charge would have to provide at least 40 W-h, and a bit more, because charging is not 100% efficient.
  • The rating of battery packs seems to me a bit deceptive: they often give the capacity in mA-h, without mentioning that the cell inside is ~3.7 volts, in most cases. A 20,000 mA-h (20 A-h) 3.7 V charger could provide ~20 * 3.5 (one never lets a battery completely discharge, lest it be ruined), ~70 W-h.
  • If that 20 A-h rating is honest, and allowing for inefficiency, that could fully charge your device once, with a dribble of energy left over.

However, many vendors are deceitful, misleading, and downright untrustworthy. One seller states its battery pack is 1,000,000 mA-h, because it can provide 10,000 mA-h each time it's used, if you recharge it 100 times!

Checking third-party reviews from a test site, such as Consumer Reports can help, but be prepared for disappointment.

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  • I never understood batteries and their physical units and what is the connection between those units.
    – fatFeather
    Feb 2, 2023 at 18:49
  • So, do you now have a better understanding?
    – DrMoishe Pippik
    Feb 2, 2023 at 22:02

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