Thought of another clock that can be wall mounted and it has a wall power supply so you could possibly adapt to 12V.. Kind of pricey but looks nice and seems to work well.
Bought this one for my Dad a few years ago, it has large numbers since he has vision problems but it IS LED.
Keeps time even when no power is applied, do far accuracy is pretty decent, Only have adjusted it once or trwice over the last couple of years since I bought it.
Power supply is a DC voltage, can't remember what voltage though but even if it isn't 12V you should be able to work around that easily.
Can get it
HERE for $50