+1 on disconnecting your battery when not in use. We own a 1991 Mustang LX 5.0, which my Wife has owned since new. It has more or less lived under a car cover for right at 20 years, now. Right before it was put in storage, I put an Optima red top battery in it. About 10 years in, we had left it connected, and the battery went flat. That is the death knell for AGM batteries, and this one was no different. We put a regular charger on it to no more avail then that I could get the car started, and then after a few hours of sitting, it would be dead. I put a trickle charger on it (made for AGM & Li-Ion batteries) for a couple of weeks, and wouldn't you know it, the battery came back to life. It is still in the car, after a total of 20 years, and if I connect the cable today, it will start the car right up.

Anyway, disconnect the battery if you're not going to drive the car for more than a few weeks.