Regarding the questions about circuit protection...
With power source 250-650V, there is possibility of high voltage and arcing in the event a component in your circuit fails. There's a risk this high voltage can reach a lead-acid battery, creating a spark inside the compartment resulting in explosion, fire, etc. Or perhaps your battery is a different type with its own hazards you must give attention to.
In agreement with your boss, it's a good idea to install protective components. Perhaps your board has a device which is expensive or difficult to replace? That is the purpose of surge absorbers, MOV's, fuses, circuit breakers, etc.