I picked up two types of USB power bank when i was in Japan last year, the Panasonic QE-QL103-K (2900mah 1A) and a Panasonic QE-PL203-K (5800mah 1.5A & Qi Charging), the other day i was curious enough to break open the smaller of the two as i wanted to see how these branded, Japanese made power banks compare to the Chinese stuff you find on ebay.
the QE-QL103 costs about £12 from Yodobashi Camera, so is not an expensive item considering it will have a good quality Panasonic 18650 cell inside.
There is micro USB for charging and a standard USB for output to devices, handily it also includes a removable micro USB adaptor that can aid charging and connecting to your micro USB devices.
It was a bit of a struggle to open, i had thought it might have been ultrasonically welded but it actually has a screw and clips. I did break a few clips getting it apart and there is sticky tape on the battery which also holds the two parts of the case together making it a bit of a struggle to open without damaging the outer case.
I was surprised by the complexity of the controller board inside, containing an Atmel XMega16D4 loads of passives and smaller ICs. In the lower right corner there is some unpopulated components, these are likely for the slightly more expensive version (Panasonic QE-PL103-K) that has Qi charging. The bare terminals labelled LP01 and LP02 are probably for the pickup coil and the unpopulated BGA device above it would be the Qi controller.
The battery and board are soldered together looping through a plastic carrier so i can only get pics of one side of the board, i did consider de-soldering the battery to see the other side but i wondered if it might not power back up when reconnected (i use this charger every day!), there could be unknown startup procedures required when the battery is connected for the first time. Considering the micro controller has a minimum Vcc of 1.6v, well below the minimum cell voltage it is conceivable that it's not expected to ever power down the micro controller. The battery also has a temperature sensor glued to it.
One thing i did do was measure the battery voltage. It turns off at about 2.6v and charges upto 4.3v so they are really pushing the max out of the cell. One thing i did notice is it seems to not draw power out of the cell all the time, when powered on and supplying power to a USB device i saw the battery voltage dropping in steps so looks like they are drawing power from the cell in pulses.
If people are interested i could bridge the battery terminals so i can remove the plastic carrier without disconnecting the battery and get a view of the other side of the board and do some more in depth poking around?
