A 14 V battery is somewhat rare but 12 V batteries are fairly common. So I would probably approach the problem with a charger-inverter between the battery and 12 V. bus. First, let's look at the expected load:
500 W / 14 V ~= 35 A. output (*)
500 W / 12 V ~= 41 A. draw from battery (rough!)
So it makes sense to go with 24 V storage and draw ~20 A for battery life. Better still, 48 V and ~10 A. But the ~35 A. output remains a challenge.
* - recent data suggests 300 W is adequate
So to design the system, I would want four, 12 V. batteries with 20 Ahr capacity to keep the expected service life reasonable. The circuit would parallel charge when not under load to keep the modules as balanced as possible. That or a well balanced charger to make sure the ending voltage is the same.
When under load, the charging circuits are isolated and the batteries put in series to a buck switcher. This should deliver 92-95% of the energy to the car and 'off load' the 12 V. source.
This is not a trivial charger/inverter to design but it isn't rocket science either. The application notes from any switching power IC are more than adequate with selection of some power MOSFETs to handle the high currents efficiently. Add a microcontroller and the problem is solved.
BTW, adding a couple of 45 W. solar cell arrays would allow daytime recharging. Think of this as an Engineer kit for the 12 V. system and one that is nearly universal. It works for any 12 V vehicle, hybrid or not.
Bob Wilson