The 18650 cell protection PCBs with 8205 ICs arrived and seemed small enough to simply tuck into the gap between the rounded cells in the second Baofeng BL-5 pack:
For whatever it might be worth, you’re looking at the only Baofeng battery pack containing an actual 10 kΩ thermistor, harvested from the benchtop Tray of Doom:
Unfortunately, the components on the PCB stuck up a bit too far from the cell surface and held the lid just slightly proud of the case. Applying pressure to lithium cells being a Bad Idea, I rearranged the layout by flipping the cells over, tucking the PCB components between the cells, and connecting everything with nickel tape instead of insulated wires:
The snippets of manila paper and Kapton tape hold things apart and together, as needed. Looks ugly, fits better.
Pop it in the charger to reset the protection PCB lockout and it’s all good again.
The Smell of Molten Projects in the Morning 
“For whatever it might be worth, you’re looking at the only Baofeng battery pack containing an actual 10 kΩ thermistor…”
Nice. I did a similar mod to some no-name battery packs for my Philips smart remote controls. Only those packs did not even have an SMD resistor, they just tied the “thermistor” lead from the header straight to ground. Made the charger get all worried.
It was an easy fix. But kind of baffled me that they would ship the battery packs in that condition.
As it happens, I just retired two of those battery packs as they were not holding much charge. Got 4 years of service out of them, though they never really seemed to meet their 800 mAh nominal spec. So I made their replacements out of some 1000 mAh NiMH cells from a name brand outfit (or what passes for that these days). So far, they are showing a lot more oomph than the el-cheapo packs did.
AFAICT, it’s a rare charger indeed paying any attention to the thermistor, even though we’re told lithium cells are so sensitive to temperature.
Sounds like you got a good charger, more’s the pity.