Thanks to a number of suggestions and posts on this Forum, I found an idea for a simple adapter* to allow me to use my cordless drill to raise and lower the tongue jack. I had doubts the drill would be up to the job, but I was amazed at how well it works. And I spent $1.39 on the whole project.
The last photo shows the 1/2 - 13 coupling nut I bought at Home Depot. This size works for two reasons: 1) the outside of the coupler fits the same socket I use for the stabilizer jack: 3/4" or 13mm. Thus I can do the trailer setup without having to change sockets; 2) the inside diameter (once I drilled out the threads) exactly fits over the crank end of the tongue jack after the handle has been removed.
All I had to do was mark and drill a 9/32" hole crosswise through the coupling nut to accommodate the bolt that once held the handle on. You can see the hole in the last photo. Then I drilled out the threads inside the coupling nut so it would fit over the 1/2" shaft on the jack. You do need a drill press and good bits for the job but it took all of 5 minutes to modify the part. It took longer than that to get over the amazement that it worked.
Thanks to Pooniel for mentioning that he had made an adapter to do the same job (different design but the idea stuck with me).
*The original post with the idea to use a coupling nut was by forum member "Jas", posted in 2010: home made power toung jack
. I had to use a different size coupling nut than he did, probably owing to the different sizes of our units.
I should mention that I have 120 pounds of batteries and two full propane tanks on the trailer, so the tongue weight is probably well over the amount it was originally.
Handle removed, coupling nut installed, original bolt reused.
My Ryobi 18v in place. The battery is only at about half charge, by the way, so ill have to be careful not to flip the trailer over with a fully charged battery...