After a recent conversation with Ecowitt support I passed on the customer request for an alternative method of powering the WS80 unit - a battery extension pack.
Support came back to me saying that modifications had recently been made to the WS80 so that a newer version will draw power from the 12 volt heater power supply if used - the same as the new Wittboy WS90 array.
Our last delivery in early April did not include this revision and asking Ecowitt further the change cannot be visually identified without dismantling the product.