While it is true a battery will lose it's charge slowly over time, the problem is the engine computer (ECU). Even with the key off that thing is running ALL the time. Takes a lot of electric to do that and over a period of 4 weeks (less on an old battery) you won't have enough oomph to get the motor started. To add insult to injury, now the alternator must try to recharge that battery so it has to run "full blast" to do it generating a lot of heat. If you only do short trips it means the alternator is always working hard and the battery is always chronically undercharged. A perfect recipe for a burnt out alternator and a premature battery failure. The "cure" is to use the car more often, take longer trips, or keep the battery fully charged with a battery tender. I have found that by putting a battery tender on the car for 1 day every 2 weeks and the night before I use it, The alternator never has to work hard and the battery lasts and lasts. If you see the headlight pods bounce when you start the car, the battery got too low. I dislike having it always connected, if it goes bad it can mess up the car.