Unhook the battery. If I were to leave for several months, I would not leave any kind of charger or appliance plugged in. Even the fridge. I would not be comfortable, wondering if some varmint chews on the power cord or something. The less plugged in, the less to worry about. JMO
I like Battery MIND-ers myself. For a car, I'd get the 1.8A one because it is small and doesn't use much wattage, so it can go on the end of a long extension cord.
I read this thread just so I could make this same suggestion.. 1-2 amps
I'd also dump in the proper amount of STA-BIL or Seafoam (I use Sta-Bil myself) and fill the tank before you park it IN THAT ORDER, Then drive at least a couple miles to get the treated gas into all the lines.
NOTE: Back when I had two cars and money.. I took off, spent a couple of months pulling "MY" car around the US,, Hopped a plane to Detroit, hopped a bus (1.75 each way) to a spot a few blocks from my house and hiked home from there.
Wife's car, With Sta-Bil and Battery Minder, fired up just like August and used this morning. (it was January).
Nothin adds excitment like something that is none of your business
Kenwood TS-2000 housed in a 2005 Damon Intruder 377
I store my collector car over the winter, and what folks have said are fine; disconnect the battery since small loads in the car will run it down eventually, and Sta-bil in the gas. Only thing I'll add is to inflate the tires to their maximum rated pressure. I do that so the tires don't get flat spots from sitting for so long.