Many years ago, Chrysler said a good battery with a full charge will be strong enough to start an engine that has been sitting for three weeks. That has become the industry standard for all cars unless specified otherwise by the manufacturer. This is due to the extremely high number of computers on today's cars. Most of them need a little standby current to keep their memories alive. In the 1980's, all we had was a radio that needed a memory circuit for the station presets and clock. Those cars could sit for months and still start.
That does not mean you cannot go more than three weeks I have a 2014 Dodge truck with all kinds of unnecessary, complicated computers. I started it twice this winter, and both times it had been sitting for over seven weeks. The second time I could tell the battery was weak, but it did still start the engine.
Also, consider that the lead flakes off the plates in all batteries over time. Typically it takes around five years before it collects and builds up in the bottom of the case until it shorts one of the cells. As the battery ages and more of that lead flakes off, it reduces the battery's storage capacity, so in effect, you have a smaller battery that will not last as long. You may not get three weeks out of it. Usually you will have other starting problems long before you have to worry about how long it is sitting unused.
If you plan on not using your car for a much longer period of time, from a couple of months to many years, there is a way to disable that standby current. (It is commonly called "ignition off-draw", or "IOD"). Most cars are shipped with part of the electrical system disabled so they can sit for a long time in assembly plant parking lots or on the dealer's lot without running the battery down, but enough works that the delivery drivers can operate them. In the 1980's there was often a medium-sized battery cable that could be unplugged. By the mid 1990's, many cars needed to have one fuse plugged in during the "new-vehicle-prep" at the dealership. Today many cars have one or two fuses in special holders that make pulling them out real easy, for the same purpose.
Be aware that some manufacturers have purposely designed in tricks to cost their customers money after the sale. Some of the computers will lock up and require the vehicle be towed to the dealer to have them unlocked. That can get to be over an $800.00 repair bill for VW owners after simply trying to replace a bad battery. Audi, BMW, and GM have the same reputation for numerous customer-unfriendly business practices. This is probably not an issue for you, but it would not hurt to double-check at the dealership. I used to attend monthly classes from a very high-level independent trainer who networked with other instructors around the nation as well as many manufacturer instructors. On their list of manufacturers with "customer-friendly" business practices, Hyundai was number one. Toyota was next, then Chrysler. That means those manufacturers put customer satisfaction and repeat business ahead of short-term profits and the need to continually advertise for new customers. I would be very surprised to hear Hyundai would stick you from simply unplugging the IOD device.
Another alternative, if the car is going to be unused for a long time, is to connect a "battery maintainer". Some plug into house current and connect to the battery. Some are solar-powered and can plug into the cigarette lighter or power outlet, but you have to verify those outlets operate with the ignition switch turned off. The industry-standard ignition-off-draw maximum current is 35 milliamps, (0.035 amps). That is about one fifteenth what it takes to run a glove box light, so it is not very much. Even the tiniest solar chargers can keep up with that. You can find these chargers at Harbor Freight Tools, hardware stores, auto parts stores, farm and home stores, and probably even Walmart.
Avoid letting your car sit for long periods on grass, especially if you are in a northern area. The condensation will rust a car very quickly from underneath.
Probably the biggest concern with letting a car sit for a real long time, as in many years, is the clutch plates in an automatic transmission can dry out. They are meant to be immersed in transmission fluid. In fact, it is standard procedure to let new clutch plates sit in fluid before they are installed during a transmission rebuild. If they are allowed to dry out from sitting with no fluid circulating, they can tear apart easily and cause debris to circulate. That can cause slipping, torn rubber seals, and sticking shift valves. To avoid all of that, it is a good idea to drive the car at least two or three times a year.
Sunday, February 26th, 2017 AT 7:40 PM