Your efforts may be totally futile. Yes, it seems dumb but a lot of motors will not start without a fully charged battery. They wont run off of a boost either because they need the battery to keep going (extra dumb).
So if your battery is dead and there is not enough juice in your trolling battery your boat is dead in the water unless you are real good with that single tiny oar you have to avoid a ticket.
This just isn't a big motor thing, the 40HPs are included. Read your manual and buy a 2 way radio.