A battery typically has, excluding the rest of the EV:

    - Around 10-20 microcontrollers.
    - Between 150 and 250 voltage sensors
    - Between 150 and 250 tap fuses with fuse blow sensors
    - Between 5-10 contactors with sensing contacts
    - Around 50-100 temperature sensors
    - Around 300 to 500 N-fet switches with balance resistors
    - (Depending on the design).. up to 300 bus bars with perhaps 600 bolts.
    - In some instances, you'll find up to 50 pressure sensors
    - A variety of interlocks and plug sensors

Aren't most of these just arrays of identical parts, replicated for each cell (or, repeated for groups of cells).

How fault-tolerant are the battery packs? I assume, with all these fuses and sensors, it should be able to safely handle a wide range of internal failures.

The packs typically have near zero fault tolerance. If there is a fault with a single sensor, they will complain and go into a limp mode or refuse to function altogether. (This is because without a single sensor, it might be impossible to detect if the pack is about to catch fire).

Also each sensor is usually at the same potential as the cell that it's monitoring. So if there is a sensor fault, it could mean that it's unplugged or has come loose. Can you imagine the risk of a dangling 600V thing flying around inside the box?

For that reason though ... I'd need two hands to count how many technicians have accidentally shorted two cells in packs together by plugging the wrong sensor into the wrong place and shorting i.e. cell 32 to 42. When this happens, it will blow up a bunch of random surface mount fuses in the control boards, and other things all over the place. You need a lot of attention to detail to tear these things down.