There you go. Like I said, they do exist, even in lower priced banks, it’s just not a widely implemented or advertised feature.
They make things like this but I haven’t tried harder to find one in-stock somewhere. Battery backup for a small device run off an 18650.
so i have a liitokala engineer charger
it occurred to me that it has a usb out, powered by cells that are in the charging bay
it doesn;t work as a UPS for 2 reasons
1. load has to be OVER X ma, and X is like 50 or 100
2. it does not work when wall-wart power is active
so it would not continuously supply 5V in either case
wle
Does anybody know of any powerbanks with pass-through charging?
The TP5100 chip used in the BLF LT1 lantern for charging can input/output at the same time. In fact, the lantern will be able to work without batteries if a power supply is plugged into the USB charging port.
Here is a simple charging board available on eBay which uses the TP5100 chip.
I think the gen2 xiaomi 20,000mAh have 5V pass through but not sure if there is a switching
when input power is disconnected. Most UPS doesn’t have switching but DIY solar controller + 12V battery charger 2in1 does. I can check it out and let you know which powerbank in my collection have non-switching pass through (always on or separated buck-boost controller).
@ Will34,
Thanks, would appreciate that!
Awesome find!
There are some more UPS especially for small electronics:
ebay.com/itm/Mini-UPS-Uninterruptable-Power-Supply-System-with-POE-Current-Transfer-Function/183952535867
ebay.com/itm/Mini-UPS-Uninterrupted-Power-Supply-7800mah-12V-2A-USB-5V-1A-Output-GM312/383191878917
ebay.com/itm/1575192-Vultech-UPS30PW-DC-Bianco-Mini-UPS-30-Watt-Gruppo-di-Continuita-Portatil/401874780975
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It would work, but it’s not available anymore: “Currently unavailable”
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They sell it in germany:
ebay.com/itm/12V-USV-Mini-USV-unterbrechungsfreie-DC-Stromversorgung-12-V-22-W-2000-mAh/122971057294
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Sure:
Blitzwolf QC3 power bank 10000mAh BW-P3, fixed version
Blitzwolf QC3 power bank 15600mAh BW-P5
Miller ML202 V4
Ravpower Turbo+ RP-PB043 (20100mAh)
Soshine E4S
Thrunite C2 power bank and charger
Tomo Power bank M2
Tomo Power bank M4
Thanks angerdan
The Ravpower looks good on review
I can’t find it for sale though.
Here it is:
amazon.de/RAVPower-20100-mAh-tragbares-Ladegerät-Technologie-schwarz/dp/B019IH53MA
amazon.de/RAVPower-20100mAh-Powerbank-Anschluss-Kapazität-schwarz/dp/B019GI39VI
heise.de/preisvergleich/eu/ravpower-xtreme-20100mah-rp-pb043-a1449786.html
My blackweb 20k mah powerbank with type c powerdelivery does passthrough
I have tested these DIY powerbanks below if they can be UPS for RPi, Routers, etc.
1. Tomo PowerBank S4 (4x 18650; Similar to M4/M2; 5V/1A input) - Can do pass-through charging but does not seem to be able to charge the battery while using the output, this maybe due to input power limited to 1A. Unplugging the input power does not cause a surge on the output USB.
2. Soshine E3S-QC (4x 18650; QC 3.0 on USB Out 2) - Can do pass-through charging, but unplugging output causes a less than a second power surge before switching to battery. While pass through charging, the USB output port 1 (5V/1A) is turned off.
3. Epilot E4 (4x 18650; 5V 2A input) - Similar to Soshine E3S-QC, but can still provide power to both USB outputs on pass-through charging.
In my case, I am trying to power an Intel Compute Stick for hotspot router. Will try this one RPi UPS with DIY battery: 52Pi Original 18650 UPS Pro Power Supply Device Extended Two USBA Port for Raspberry Pi 4 B / 3B+ /3B
The following stuff is advertised as UPS, besides being a DIY power bank meant to provide power for up to 65 W laptops:
https://www.aliexpress.com/item/4000268838287.html
Battery arrangement is 3S2P, but if I were to buy one I'd make windows on the cover and install more batteries (of course all soldered or spot welded).
There are some related videos out there. 
thanks
Some are said to work starting cars. True?
Some car starters offer 200-400A.
https://enerprof.de/en/portable-energy/powerbanks/28/tensai-tb-13600-car-jump-starter/power-bank
Do you have any links to those videos please?
Lots of possibilities out there, important question.
e.g. https://www.instructables.com/id/DIY-Mini-UPS-for-Router-Modem/
I’d like to see a reliable answer.
Nitecore F1