i didn't downvote but 17v on a 12v battery maybe seems a bit high. I'm more used to about 7-14% over (maybe up to 14v on a 12v batt) when charged/floating but i don't use solar anywhere currently, and i usually work on 48v systems. i normally expect to see about 54v on a fully charged battery string (13.5v per battery x4) with the rectifiers running.
i also second the opinion of running an automotive PSU for this situation.
edit: i looked it up since i was curious, some "12v" solar panels can output between 16-20v, but it's recommended that you would use a charge controller, especially if you have lead-acid batteries
the view may have been "if you blow up the tracks you can't use it either" but i have always wondered this. even today you still see armored trains but in "peace" time you probably have to worry less about sabotage of the tracks and more for surviving ambushes