The best thing is probably to start by checking current drain. Then figure out how long it can be left connected without depleting the battery. If it is significant, you can get battery disconnect switches for about $5 at Harbor Freight.
You can also make a very good solid state switch with two MOSFETs. You tie the sources together and the gates together, and add a 10k resistor from the gates to the sources. The drains will be non-conductive and constitute an open switch with typically less than 10uA leakage. The drains, which are the tabs, can be used as the switch contacts to the battery. If you apply a voltage, like 9V or 12V from a small battery, to the gates, they will both turn on. Here is a 100 amp 40 volt MOSFET with about 2.8mOhm RdsOn for about $1.72 each:
At 60 amps they will each drop 0.17 volts and 10W, but that's at maximum charge/discharge and at more normal levels it's much less. There are of course many devices available so you can choose voltages and currents as needed and parallel devices to get lower resistance.
You could also use an optoisolator to turn the switch on or off using some other signal such as the ignition switch.