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I've been checking all the questions and can find many similar ones, but unfortunately none that addresses my problem. I ended up reading many interesting questions and answers (including e.g. this one Can i connect Power source (like usb charger) parallel connection with power bank output for keep Uninterruptible power supply (UPS))

I however already have a few PowerBanks mainly something like this. I would like to use one of them as a ups, but my problem is it does not seem to charge when it is charging. Is that a "feature" of the battery, or is it to "protect" me from wearing the battery down? How difficult/dangerous would it be to disable that feature? Could i just go ahead and get the power directly from the end-poles of the batteries bypassing all circuitry, or that would be dangerous?

Last, I have a second brand of powerbank, this one. Here things are even more complecated, as the battery requires me to press a button for it to start charging... Is this standard?

I have seen it be done, since I have found that there are similar power banks out there that can fact provide while charging e.g., with other power banks, e.g. http://raspi-ups.appspot.com/en/index.jsp. It also seems to be an "ok"-ish thing to do (https://www.quora.com/Is-it-okay-to-charge-your-phone-through-a-power-bank-while-the-power-bank-itself-is-being-charged)

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  • \$\begingroup\$ The part of the power bank that charges the battery is almost certainly separate from the part that provides a nice regulated 5V output. With that in mind, yes, charging while in use should be ok, but in reality what happens is the charger is powering the 5V regulator directly (and may even do so without a battery at all, but only the cheap ones have this "feature") \$\endgroup\$ – Sam Feb 15 '17 at 1:20
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Power banks are a class of devices to serve as emergency power sources in stand-alone mode. You charge it, and keep in your briefcase just in case. As such, most power banks are not designed as UPS (uninterruptible) supply. While some banks can do this by design (as the OP has discovered this himself), it does not mean that all power banks would charge its internal battery and provide power to output port. Some power banks even provide a warning label, saying "Do Not Charge & Discharge At Same Time!!!"

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The powerbank can not be modified as UPS without replacing its active electronic circuit. The new circuit must contain the charger for battery with direct path to VBUS, AND an additional automatic power switch from direct feed to the battery booster to OUTPUT if external power is lost. Texas Instruments has a sizable portfolio of PMICs (Power management ICs) where this function is integrated into controller IC, as BQ24075 for example. Other manufacturers as Linear Technology, Maxim Integrated, Richtek and others have similar ICs. This board from SparkFun can likely do the job.

ADDITION: Here is a solution for 1-cell UPS offered by Maxim.

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The power bank will not power the targe while charing. The reason is simple: The wall wart (power supply) is not able to deliver enough current to do so.

Most will also use standard USB cables which do not allow much current above 2A.

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    \$\begingroup\$ I would be ok if there was enough power once the battery was not full, I am mainly interested to use it as a ups, so it should provide power while the battery is charged... That said, i think it should be doable because people have done it... (added relevant url of the project in the question) \$\endgroup\$ – ntg Feb 10 '17 at 14:39
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You can get bypass enabled POWER BANKS. Otherwise, it's not possible. Only few power banks support it, we can charge while its in charging mode. MI power bank supports it, and it also supports the Quick charge3 for Qualcomm Processor phones.

Example: MI Powerbank2i
Link: https://www.mi.com/in/10000mah-mi-power-bank-2i/

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  • \$\begingroup\$ I believe the question was if his powerbanks can be modified rather than buying a new one. \$\endgroup\$ – Sven B Jul 9 '18 at 11:02
  • \$\begingroup\$ If you have the Mi Powerbank 2, can you confirm that it does not reset when power is restored? My Mi powerbank, after running on battery, when external power is connected, it cuts output for 1/2 a second - which basically power cycles my Pi. \$\endgroup\$ – Colin Aug 26 at 7:55

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