I have a 1994 F-150 truck that has some electrical problems. Notably, there are the remnants of an alarm system in it. This alarm system also has a kill switch function that at times disables the truck.
Since I use this truck infrequently I’ve battled this alarm and the battery draining for years. I have tried a couple of times to have this alarm system removed, but have been unsuccessful in finding all the parts. Therefore I’ve resorted to addressing the symptom rather than spending any more time, effort and money to remove the alarm system. To do this I installed a battery disconnect switch. A couple of quick turns of the green knob either connects or disconnects the battery from the electrical system of the vehicle. Now when I want to use the truck I tighten of the knob and it starts right up.
Anyone who has vehicles or tractors that are used infrequently may find such a disconnect switch to be of value. Of course you lose any saved settings in something like a digital radio, but to not have your battery drained is worth it. Many newer vehicles have phantom loads that consume power, in small amounts, but never the less are there. I have heard that the Toyota Prius has something like a parking or storage mode where the engine will start periodically to recharge the batteries. I suspect this has a much bigger phantom load than other cars. Older vehicles should have no phantom load.
Lead Acid batteries do have a self-discharge rate of about 5% per month so you cannot just disconnect a battery and expect it to stay good forever. That is why there are such things as trickle chargers, to keep batteries topped up and keep the batteries from being damaged by discharge. Take care of your batteries and they will take care of you.