I send batteries to anyone. It doesn't cost cost me anything. I rarely even check the names. I just hit send all. I'd send to everyone on the server if there was a button for it.I even less seldom check who beat me in duels. I've had some nice exchanges with people after duels or studio fights. A little smack, a little flirting *shrug. Long as they aren't being rude in the messages. Then, I might block them or tell them to buzz off.
As far as dueling, I pick duels I'm pretty sure I'll win. If I have missiles off to save for studio fight, I may go further down the list. Not as much glory and notes but surely more than a loss, and some of them do still award items and diamonds.
On one server, I found a studio-less wonder that is good for 3 easy wins every time I need duels for a task. some weird name that is just random letters. They must login because they don't trigger the no hits message when you go back to the list. at same level, I was one-shotting them without missiles on. No glory win, but it counts for the daily task