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cany you just use the wall plug in that you charge the battery with.
so basically if I understand you correctly, you are looking for something like this: http://www.amazon.com/Roadpro-Fused-Replacement-Cigarette-Lighter/dp/B0016LG0CY with the end connectors being spades that fit into the ones from your vexilar (or whatever connector type the vexes have if special). I am also assuming you want this instead of directly hard wiring to the battery because you already have it in a powerbox with a cigarette lighter adapter in it??? If not it would be easiest to just make a couple of wires that have a connector compatible with your battery posts crimped on one end and a connector that matches your vex cables on the other (assuming the vexes have a fuse already built on to their wires like my lowrance ff does).
maybe a power inverter to run your charger from a 12 volt.what kind of connector does the unit use, a coaxial connector?
That's what I do. I have an inverter that plugs into cig. Lighter.