I've started up a little hobby of taking apart laptop Lithium-ion battery packs that have kicked the bucket. Why? At work - I design some fairly similar circuitry and like to steal ideas "from the pros". Mostly it's interesting seeing what ICs and FETs they choose for these mass produced devices.
There's one part that I've encountered time and time again, and I simply can't explain it. It is always situated right above (literally above) or right next to two back to back FETs (or two paralleled back to back sets of FETs). It always has some sort of white crud between it and the FETs - probably a thermal goop of some sort. It is a three pin device. They all look about the same, though the package varies from board to board. Sometimes some of the pins show shorts to each other, sometimes not. This may be due to shorts on the PCB - I've never pulled the component to find out. I've seen this on PCBs that are only a year or so old, and most recently, on a PCB that was something like 10-15 years old.
I've attached some photos of it. The 8 pin SOICs are FETs. Also note the flux residue on the PCB on the leads - messy enough that it could have been hand soldered maybe?
Anybody have any ideas as to what this bugger might be?