Most  EVs and Hybrids have at least three contactors.  The sequence is:
* Close One battery lead  and check for leakage
* Drop that relay and close the other lead with a series resistor and
check for leaks
* Bring the first one back in to power up still via the series resistor
for a few milliseconds to allow the car system to charge all capacitors
* If still no smoke, pull in a main contactor to bypass the resistor.

You can hear the relay dance in any Prius or most other EV's.

There should be NO heavy loads until all of the above are complete.  A
software glitch in the THINK CITY made the mistake of leaving the 4 kW
heater possibly on, so that on the third step above, the 4kW is trying to
go through a 5W 47 ohm resistor and it blows up.  This kills the car, and
all replacement b0oards are gone, most cannot be repaired, and so the
company is out of business and there are lots of THINK CITY's  just
gathering dust.

Bob, WB4aPR
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