How to fix 2 flourescent lights in caravan that don't work?

Last week all lights in our caravan were working good on 240volt power, but after trying battery to see if power with battery worked, the 2 flourescent lights stopped working,have not worked since, 2 bed lights and kitchen lights all work, except the flourescent lights in caravan, we don't know why it is only the flourescent ones, have changed with new ones, makes no difference, need help,please?