Teardown: $15 120V battery pack

[NiHaoMike]

I got two of those $15 120V battery packs after finding this post on Hackaday:
https://hackaday.com/2018/03/07/desperately-trying-to-find-a-use-for-the-chugplug/
The unit I got is obviously a newer, "cost reduced" version than the one in the video. (Mine has no vents and the power button is in a different position.)
Summary of teardown:
* The case, as expected, is very difficult to open and even more difficult to do so in a manner that allows it to be reassembled.
* The output DC/DC converter is some strange combination of a boost converter and forward converter, with no intermediate DC voltage between the two. It outputs 120V DC, a bit on the low side for its intended use. Will scope/reverse engineer that more when I have time.
* The battery is 2S 8Ah. The case says 3.7V (1S) 16Ah. Maybe the printing stencil was done before the EEs figured out that 1S would run at too high a current for a workable design?
* The charger is a balancing design with two stacked outputs. It gets quite hot when charging, not at all desirable next to the battery. The extra diode drop wastes far more energy than a resistive balancer, which, contrary to what many think, rarely even comes into play if the batteries are in any decent condition.
* Neither the charger nor DC/DC are isolated. Not required in its stock configuration, but beware for modding! The EEs must have figured out that the cost savings from not having isolation outweighed the additional sales they could have got adding a USB output.
* Once switched on, it requires about 8W of load to stay on for more than a minute or two.

Comparison to older version based on online posts:
* The older version has a 3S 4Ah battery and a pure sine inverter, most likely an off the shelf design modified to fit the shape. By eliminating the inverter part, they made room for a larger battery and increased the efficiency. A big win for its intended use.
* The older version would stay powered up when unplugged so it can be used as a small UPS. The newer version switches off when unplugged making it useless as a UPS.

As for uses, one that comes to mind right away is to power a glue gun for use away from mains. The DC output precludes using a soldering station (or anything else) with a transformer, but those are on the bulky side for portable use anyways. What I really don't like is how hot it gets during charging, so I'll probably end up tearing down the second one as well and using the parts for projects.