Originally Posted by stevemoores
I think I was over thinking this.
My concern was connecting the charge line direct to the relay then to ground would draw a huge current from the battery through the relay coil and I'd have to limit it somehow (externally with a resistor).
I looked online and found that most automotive relays have a coil resistance of around 100ohm, so at 12v, that's a current draw of around 100mA. Shouldn't be causing any fires.
Happy I cleared that up
You were overthinking it. 12 volt relays are exactly that, designed to be connected across 12 volt supply.