That is actually very difficult to answer because a lot of changes took place around the mid 2010s. Going back to the 1980s when computers started showing up, they had a very small current drain to keep the memories alive when the ignition switch was off. Chrysler called that "ignition-off-draw", or "IOD current". They allowed up to 35 milliamps, (0.035 amp), and said with a good, fully charged battery, it would still have enough charge to crank the engine fast enough to start after sitting for three weeks. Today that is the industry standard unless stated otherwise by the manufacturer. Cadillac, for one, allows up to 50 milliamps. Three weeks is the advertised limit. In practice, for my '93 Dynasty that gets stored for long periods, it has gone well over six weeks and still started fine. To put this in perspective, a little # 194 "peanut" bulb often found in glove boxes draws close to half an amp, (0.500 amps), or 500 milliamps. When left on overnight, that drain can be enough for the engine to not start the next morning.
How long you can let the vehicle sit depends on the electronic options it has that need a small current to keep the memories alive, how old the battery is, and temperature. The lead gradually flakes off the plates over roughly five years. Only what remains on the plates is effectively the battery, so as it ages, electrically, it becomes smaller and smaller with decreasing storage capacity. You may not get the full three weeks with a three or four-year-old battery.
Lead / acid batteries are a chemical reaction, and those always slow down as temperature goes down. In cold weather, a battery is less able to develop its full rated current. Add to that the engine oil is thicker making it harder to rotate the engine. Without going into a lot of electrical theory, (unless you want me to), a starter motor that is loaded down draws higher current. To illustrate this, with an older GM or Ford V-8 engine, the starter motors typically draw over 300 amps at first, then once it's up to spinning the engine at normal speed, that drops to 200 - 250 amps. When cranking in cold weather, that can go over 400 amps to get going, and will drop once spinning. This is where a weak battery shows up first. Much of the damage, (wear), takes place in hot summer weather, but shows up in cold weather when more battery power is needed and when it is less able to develop it.
The next issue is vehicles as new as yours typically come with a new type of battery called "absorbed glass mat", (AGM). They do not use a liquid electrolyte, but they still do generate hydrogen gas. In liquid acid it's easy for that gas to float up and be vented out. That is more difficult in AGM batteries, so some means of limiting charging current is added to the electrical system. Regardless how run down the battery is, and regardless of the charging voltage, charging current is limited to a safe level. That is lower than we saw years ago with standard batteries. As a result, we're kind of back to the problems we had before Chrysler developed the AC generator for 1960, (aka "alternator). With the older DC generators, short trips weren't enough to fully recharge the battery. It wasn't uncommon to have to charge the battery with a portable charger once or twice a month. I had this problem with my 2014 truck two winters ago. I made daily five-mile trips. After a few weeks, I had a battery too weak to crank the engine. With older, standard lead / acid batteries and no charge current limiting, five miles would have been plenty to keep the battery fully charged. This year I make at least weekly trips of up to 40 miles. The battery is getting old, but there's no issue with it running down.
There's two things you can do to address this issue. At first, Chrysler had a smaller positive battery cable with a large bullet connector that could be pulled apart to stop the IOD current. New vehicles were shipped that way so they could remain in storage for long periods. They could still be driven, but some electrical things didn't work, and safety systems like power windows and wipers might only work once the engine was running. Everything needed to drive the vehicle onto and off of a transport truck would work.
In later models, somewhere around the mid 1990s, they went to a fuse instead. It was taped to the fuse box cover and got inserted at the dealership as part of the "new vehicle prep".
Today it is common to incorporate the IOD fuse with the Air Bag system. Anything related to air bags is colored bright yellow. In the under-hood fuse box, you'll commonly find a small yellow plastic holder around two fuses. The holder makes them easy to identify and easy to pull up to disengage those fuses without misplacing them. Anti-lock brakes and air bags always have two fuses and two power supply circuits to those computers. That's so if one fuse blows, the second circuit lets the computer operate enough to turn on its warning light on the dash. By the way, those fuses are also commonly tied in with other safety systems. For example, Chrysler powers their rear wiper motors through one of the air bag fuses. If a short develops in the wiper circuit, you'd never know it until you need it and it's too late. By blowing the air bag fuse, that warning light turns on so you know something needs attention.
The air bag fuses are in that yellow holder in the fuse box so they can be quickly identified by fire and rescue personnel. They pull that so nothing they do can accidentally pop an air bag. (That's actually extremely difficult to do, but with lawyers chomping at the bit, every possibility has to be accounted for). That holder also makes it easy for you to pull those fuses when the car will sit for a few weeks.
I should stop here and mention too that for most vehicles, you can simply disconnect the negative battery cable. You may have to reset some things like the clock later, but "customer preference" settings are usually maintained in a "non-volatile" memory in the computers. That means things that were programmed on or off, like speed-sensitive power door locks, and the digital gauge readouts you selected for the instrument cluster, are maintained in memory even when power is removed. Remote key fob learning is also maintained. The glaring issue here has to do with some manufacturers that purposely design in "got'chas" that force you to have the vehicle dragged onto a flatbed truck and be hauled to the dealership to have multiple computers unlocked. BMW, VW, Audi, and I've heard a few GM models fall victim to this. As a result, the people at all battery stores will always plug in a memory maintainer when they install a new battery for you. I know from experience that my 2014 truck and 2014 minivan are not affected by this. I just reconnect the batteries in spring when they come out of storage, and only have to reset the clocks.
The simplest solution to all of this is to use a small battery maintainer. I bought four of them from Harbor Freight Tools. You can find them at any hardware store, auto parts store, Walmart, etc, for less than $20.00. I leave one connected to my truck's battery, with the power cord hanging out the grille, like we used to do years ago with engine heaters. I've seen these rated for one amp, two amps, and even as high as six amps. Mine can develop up to two amps which is more than necessary for most applications. Unlike regular portable battery chargers, these maintainers lower their charge current when they see the battery is showing a full charge, to prevent overcharging.
You can also find solar-powered battery maintainers, but the vehicle has to be parked in sunlight for them to work. I've never worked with one of those but I hear they do work. The ones I've seen plug into a cigarette lighter outlet or power outlet inside the vehicle. If you use one of those, the outlet has to remain live when the ignition switch is off. On most import models, cigarette lighter outlets go dead, when the ignition switch is off. On my two 2014 vehicles, the power outlets are powered through fuses that have three holes in their sockets. You can choose to put the fuse in two terminals that go dead when the ignition switch is off, or you can move the fuse to the other terminal so the outlet stays hot all the time. That would let the solar maintainer keep the battery charged, with nothing to connect under the hood.
I have one more comment of value to add. Regarding running the engine to recharge the battery. That is better than nothing, but you'll likely still be in for some frustration. The biggest issue is all generators require three things to work. They need a piece of wire, a magnetic field, and most importantly, movement between them. In the generator, we use a coil of wire to increase capacity. We use an electromagnetic coil of wire to make the magnetic field because it is real easy to adjust their strength and control charging current and voltage. We spin that electromagnetic "field" coil with a belt and pulley to get the movement.
Because of the need for movement, all generators are very inefficient at lower speeds. In fact, at idle, the electrical system is likely to draw more current than your generator can develop, leaving nothing left over to charge the battery. The battery may actually be discharging slowly while the engine is idling. When we use a professional load tester to test charging systems, one of the steps requires we run the engine at 2,000 rpm. At that speed, the generator can develop the current it is designed for. It will not be capable of developing more current than that at higher speeds.
Thursday, March 5th, 2026 AT 3:40 PM
