I have compared the oled versions, and the one with case has a bigger display with one digit more on capacity and power. Lol unsure if anyone is better in total…
It works good and it is fun to actually see how inefficient these USB power banks are…
Sad is that if you measure a power banks capacity in total the device will shut off after power down and loose the mAh value so you need to check it from time to time to see the result, haven’t thought of that until it was too late.
The last one linked does not suffer from this.
It does indeed shut down after the powerbank is empty but it has memory function so if you hook it up to another usb source, (a new powerbank or computer usb port or wallcharger or whatevery) it will show you the mAh count. And if you don’t attach a load to it it won’t add more to the counter.
They are not that inefficient, if they deliver 65% of battery capacity they have good efficiency.
I have one well-reviewed powerbank (Coolook), and it sometimes fails to detect insertion of USB-stick LED lights. I’m guessing the power banks have a threshold for detection of the presence and some devices don’t signify.
It’s all a question of the perspective… I got around 60% ratio of the mAh in the small one I have in my edc bag. So it isn’t so bad at all if 65% is good. 
It would be cool if these things would measure Wh because I recognized on some power supply’s the voltage rises if you pull out more current…
The problem is that the rated capacity is for the battery, that battery only has an average voltage of 3.7 volt. If the boost circuit was 100% efficient the output capacity would be 74% of battery capacity (With a 3.6 volt battery it is 72%).
A Wh rating would get around that.
Thanks for the explanation, now I can understand what you meant.
I just compared the mAh I charged in my phone with the mAh I filled In the power bank to charge it up again.
I also depleted it totally but like I said above I didn’t thought about the fact that if the bank shuts off I loose the info.
I will do that again if I have time to monitor it continuously, the cell inside is a single ncrA so it shouldn’t take too long on 1A load and probably 80% efficiency 0.74*2.9*0.8=1.7Ah. ->1h43min
using the usb doctor’s readout? depending on the voltage sag the mAh would be comparable, but then you are influenced by buck+boost+charging inefficiencies?
i have been interested in using it for gauging the capacity of e-cig batteries while charging. the results can vary quite a bit depending on the capacity class and charging circuit. i wonder if there is a typical formula for estimating it.
The charge circuit in a power bank is often a linear regulator, i.e. for a 3000mAh battery you need to fill 3000mAh into the box.
that is surprising. what would be the logic for that?
on an unrelated note, does anyone know if these types of oled displays will fade if left on for long periods at a time?
It is cheap and gain from using a switching regulator is not very large.
When charging you are not supposed to be limited in power. If you are using solar cells the that is, of course, not correct.
LCD does not fade, but oled does.
FYI folks…
Inline/passthru DCP enumerator
This is a passthru single port version of what I built, well…other than using the power provided by the port of course…mine uses an external power source
Truthfully you could take a standard USB cord, open it up around 1/2 way down, short the D+ and D- cords together and the device will pull up to a max of 1A then heatshrink it closed again…a “5 watt dedicated charge cable”
This looks nice too. KCX-017 $5+ (Aliexpress). Voltage, current and discharged capacity values shown on LCD display.
Gearbest selling it as well, $7.55 << WE NEED GROUPBUY for this!!! <Hint>
I might get one of those from aliexpress
I just received one of those from an ebay seller. Took them about two weeks to get it to me.
The display is a little small and a little hard to see in full daylight, but it seems to work pretty well. I like the memory feature. The OLED meters aren’t much good for seeing how much a power bank can deliver since they forget when the power is cut.
I’m a little suspicious of its accuracy though. I need to rig up some sort of test harness and check things against a multimeter.
Apologies if this has been posted, but this video includes a demo/review of that Matek meter from Bangood. It doesn’t sound like it remembers its readings after the USB power bank shuts down.
Price matched and down to $6.27 regular price from fasttech
https://www.fasttech.com/products/1004/10009801/1859500-kcx-017-usb-terminal-power-adapter-voltage
Won’t find a much better deal for this really good charge doctor anywhere
cool, has a display too…nice
^Seems kind of pointless to support up to 10V, we need 20V capable meters for the new USB (3.1) Power Delivery spec. :bigsmile:
Btw I came across this site, which did some pretty in-depth testing of various usb meters, it’s in Chinese however. [心得] 幾款USB電壓電流測試器準確性測試 - 看板 MobileComm - 批踢踢實業坊