mystery setup to explain. previous user plugged batteries in a weird way . how to explain it

Hello everyone.

I am having a hard time to understand how the previous user set up the 2 x 12 v batterie in this 24v weelchair and why?
is there advantage , disadvantage to set up the wires like that instead of one anderson connector per batteries each going to the chair independantly.

Also there is the wire with the 2 little balls going from neg to pos. Isn't that supposed to shortcircuit the batteries( each batterie has a 2ball wire.)
video is
manual i tried to put on archive.org : https://archive.org/details/s646se.196pages

chair is quickie 464 se

Thanks