This has spiked my curiosity...
If I understand correctly so far, you are developing a device that is to be installed in a vehicle, right?
So my question is:
Will this device be continuous ON?! Like, even when the vehicle is parked overnight?
If the device does not need to be continuously powered on, and only needs to be on when the vehicle is in use (key in the ignition), then my advice is to take of the battery, and power the device through a circuit to allow for some safety feature for when the motor is started, and for a more "clean" way of powering it off.