I had a quick look at this several years ago.
I found a curious thing: none of the "nice" electric ones that I found were variable speed. All the variable speed ones were petrol.
Maybe it has changed since, but it's worth checking explicitly. But all the hangar people I see have petrol tugs.
Lots of people have tried to buy electric tugs from the USA but the vendors reportedly won't ship them without the batteries (which are only simple car batteries) which makes the freight costs silly.