[ Edit: I neglected to mention that this detector resides inside the iMiEV battery enclosure. ]
I've seen this described as a "battery detector"; I'd say it's actually the battery leakage / insulation detector. Note the long plastic legs separating this device from the metalwork. (The mounting holes are cropped off in this photo, sorry).
Here is the PCB from above:
Two components stand out to me. The thing that looks like a battery (especially with code BAA3 on it), but it seems to be a zener diode, ZD8.
And this rectangular thing, that initially I thought was a PCB relay, is a capacitor, C13, 1 μF, presumably with a very high DC voltage rating. It connects from the double insulated orange cable to "earth" (the large area under the PCB, connects to what I assume is pin 1 of the 5-pin connector).
I count 6 8-pin chips, one (the smallest, marked LTTH e3) by Linear Technology, and three by Analog Devices (hence, quality and expensive). It seems like a lot of electronics just to measure insulation leakage. I'd love top know if this is way over-engineered, or just what it takes to make a reliable EV. [ Edit: the "e3" isn't a part number marking code, it's a code for the finishing of the leads. So that's no help. But see several posts down. ]
[ Edit: modified last paragraph to add "LTTH e3" and the mention of Analog Devices.
Changed subject insulation -> leakage. ]