Also depending on your usage pattern you may need to periodically use a 12v trickle charger(battery tender) to keep the 12v battery topped up as a standard lead-acid 12v battery doesn't like to sit low in charge for extended periods of time. Because of this some Leaf users either replace their 12v lead-acid battery with a much more expensive lithium battery or what I did, replace mine with a somewhat more expensive AGM battery like an Optima yellow top battery which is better suited for sitting for extended periods of time at a lower SOC.
Of course, you could always just use a standard lead-acid battery and be religious on hooking up a 12v battery tender, preferably whenever you charge your main traction battery. Some have even hooked up a quick connector for the 12v battery which they run under the charge port, plug in the J1772 and plug in the 12v battery tender, easy peasy.