I faced same issue in my lucida, yours is a very smal portion. mine is like spread all over, even sone spills out of the bonnet. When battery gets weak and stop accepting full charge, acid gets sprayed. I have left it alone, no rust developed so far.
Keep checking battery position perdically. IN my case, A Respray in such areas is difficult because of all the gadgets around. Youc an get it done easily.