I just installed my electric jack and it has a rubber top cover or plug that is where the jack handle for manual use would be inserted. I actually pulled that plug and simply used my electric drill with the right size socket attached to it and it lifted the trailer up and down very easily. On my E-Pro 19FD, it takes about 100 cranks to manually life the RV to full extension. Not a fun task if you have arthritis as I have. The electric tongue jack is a real blessing for me.
When tying it into your batteries though, be sure to put the one positive lead onto the battery with the least amount of cables attached to the lugs, as you want to evenly distribute the load for each battery to lessen any chance of your batteries eventually playing out one before the other. I used extra long and extra heavy zip ties from Lowe's to keep that positive wire from dangling below the hitch area.
2020 19fd affectionately named Harvey, as in saying the word RV very fast and after the James Stewart movie, Harvey. :-)