Automotive Grade Power Supply
At the input side, you need to accommodate potential accidental reverse polarity (somebody connects a battery the wrong way around), voltage dips and spikes, and "load dump" (the alternator output suddenly losing regulation and reaching 60V or more). You need to ensure the unit cannot drain the battery when the ignition is off.
Internally, you will need to ensure the unit complies with automotive standards for Electromagnetic Compatibility - that a certain level of external conducted or radiated interference over a specific frequency range doesn't adversely affect operation (or if it does that it fails safe), and that it does not emit interference by conduction or radiation. Compliance to the appropriate standards will need to be independently tested and certified.