[_paralyzed_]

it doesn't need to be equal voltage per side. a series connection is like a flashlight- positive to negative to positive to negative, so, to make a series connector you need two male plugs (to batteries) and one female (to esc). The female plug will have the positive from one battery going to the positive side from the connector AND the negative from the other battery going to the negative side of the connector. So, you have half a series connector now, positive from one male to positive of female and negative of other male to negative of female. Now all you do is put in a jumper wire from open negative of male to open positive of male, connecting the two male plugs. sorry, without illustrations this could be confusing.................................