Cooked pancakes keep 3 days refrigerated and freeze for 2 months — stack with parchment between so they separate. Reheat in a toaster, which crisps the edges. Don't keep raw batter overnight; the banana oxidises and the leavening goes flat.
The pan is too hot. Banana batter browns fast because of the sugar — cook on medium-low and give each pancake 2–3 minutes before flipping.
When bubbles form across the surface and the edges look set and matte rather than wet. Usually 2–3 minutes.
Not with banana — it browns and the texture suffers. Mix the dry ingredients ahead and add the wet in the morning; that takes two minutes.