I specifically picked this power bank for the LiPo cells. The power bank is functioning fine and I have no complains but I have noticed one little quirk.
When the power bank is off, the blue port has no power at all, meaning that if you plug in a USB power meter it doesn’t measure anything. But in contrast the other port on the power bank, labeled as USB2, measures a voltage of 3.67V.
In short with the power bank off, the secondary port has voltage when the primary port (blue) does not. When you turn the power bank on, both ports switch to 5.25V.
My question is, if this is normal or not? Can anyone else confirm this is happening on their power bank and if so what’s the benefit of such a design.
For the record, the store I purchased the power bank from has confirmed that this is happening with all of the samples they have. So it’s not a problem specifically tied with the one I purchased.
They usually have 2 different controller ICs, 1 for each port when dealing with QC vs regular USB. I assume one just disables the boost circuit and leaves the output connected direct to the internal battery.
It’s just a quirk. The only thing to worry about is if the cells are still protected when the unit is turned off or you could end up over discharging the cells e.g. by using a dumb load like an LED
Well, the measuring system is just 4 leds on the power bank. I am not sure if estimation is based on voltage but the power bank is brand new and probably needs a cycle or two.* The cells are advertised as LiPo if that makes any difference.
It would be interesting though if by just plugging in a USB meter you can check the voltage on the cells which would make it much more reliable than a rough estimate every 25% for each led on the power bank.