I'm going to go out on a limb here and make a couple of generalizations... One is that from my experience in the bike world... people who notice a cup holder first thing drink and ride a lot! I was hoping thats what the using both hands thing was about, which for a drunk used to riding with a beer in one hand all the time is a great safety upgrade, but not sure sure after the passive aggressive response from him.
Another assumption is that he maybe didn't notice your cool double battery holders that are already low slung on your rack. I'm guessing he thinks the battery is up higher in the cargo box.
Separate double battery question... do you switch between them? If so, I think you'll find if you carry both of them all the time anyway, may as well leave both hooked up, as it reduces the load on each cell in the batteries, and wastes less in heating up.
The third generalization is that riding with both hands is way way over rated anyways....