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.
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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