For some reason, commercial EVs tend to have batteries that run in the 300-400ish volts range, whereas conversions tend to be more in the range of about 100 to 200 volts. Lower voltage means more amps which means thicker wires [1], which are kind of heavy and expensive but it's not generally a huge problem as far as I know.

[1] https://www.evwest.com/catalog/product_info.php?cPath=2_21&p...