Speaking of the protection board: this is a Shenzen Dalishen Technology DDJ10A9.

The board in their product photo got a much better soldering job than ours.

The four large components are MOSFETs (by GuangDong Mosfet Semiconductor Co., Ltd.) responsible for charging and discharging, and have pretty skimpy solder joints.

So far this is the only sketchiness we’ve seen, although it is a bit concerning. These particular solder joints are going to see a lot of power as the battery is charging and discharging.