Car Batteries in the Apocalypse

Hi to all you knowledgeable folks. I’m a writer and working on book two of my zombie apocalypse series.
I know that the longer a car sits, the less likely it will be to start, due to the battery draining. I’ve also read that it very likely would be impossible to jump start a dead battery after a certain amount of time.

I’d love to pick (not eat!) your expert brains about the length of time you feel it would take for a battery to drain completely. Would some vehicles start on their own (or take a charge) after, say, five months? Would an older car/truck with less electrical systems to maintain (like radio, clock, etc.) be more likely to start without a jump?

Any other information you feel would be pertinent would also be appreciated. I know it’s an odd question, but I need some good advice–I hate to get my facts wrong. Thank you!

Just personal experience here but I left a vehicle on a storage lot for 18 months out in the elements in Washington state. The original plan was for only 2 weeks but we stayed a lot longer in Alaska due to family reasons. The vehicle started right up when we got back and ran just like it had 18 months prior. I’m sure that some batteries would last for years if they were disconnected in the vehicle.

I think you can pretty much pick any time limit you want up to a year or two. I’ve had them go dead after four months disconnected and still ok after 6 month connected. Never let one sit longer than that though and still usable.

Thanks, Missileman. Wow, eighteen months? That’s good to know. My father’s car battery died in a few months while sitting in the driveway. It took a jump, though. Maybe it has something to do with the age of the battery as well?

I know disconnected batteries will last, but a lot of these fictional abandoned cars belong to people who are now zombies, so they definitely didn’t take the time to do that. :wink:

Thank you, Bing!

I’d say to look at it more like “odds” than anything cut and dry. The odds that any battery has enough juice to start a car decline over time. It declines more with weather extremes (hot and cold). It declines with the age of the battery, and it will decline more in newer cars since they do have things that draw a little bit with the car off. It will also even depend on how good the battery cables are. Figure you put 10 random cars off the street in a lot that were all running when parked. After sitting for a year, maybe half of them would start fine without any help. A couple more might roll if you cleaned the battery connections. The others would need a jump or a new battery. I’ve never done that - so nothing scientific there. Just a general idea.

Why are you concerned? In a supernatural world where the living dead walk, why can’t they bring a dead battery back to life?

In a zombie apocalypse, there’s also going to be whole Walmarts full of unused batteries. I’d take one along with me while I go hotwire the nicest car in the lot (edit: I mean, the most easily stolen car. I don’t know how to hotwire, so I’d need an old jalopy you could start with a screwdriver). (edit #2: or find a dead zombie’s keychain and wander around pressing the unlock button until I find the car)

I had an interstate deep cycle marine battery in a 79 Cutlass that started up after almost 13 months.

Here’s what you do: The protagonist finds an old car with a manual transmission parked at the top of a hill. S/he turns the key to the run position, puts it in neutral, pushes it a little to get it rolling down the hill, jumps in, pushes down the clutch, puts the transmission in first, and pops the clutch. No juice needed from the battery. Now, there’s still the problem of the gasoline having gone bad if it’s been sitting too long…

My boat battery goes 9 months, but the trickle charger does take a few hours until it is good again. It is a 10 year old battery. Some factors include drain, my boat has none but a typical car will have some and it will vary from model to model. There is no reason you could not disconnect a battery and jump start the car, but putting a new battery in would be the best choice. I would consider 7 years the max limit.

Some car battery numbers fyi. A typical car battery, fully charged, stores about 30 amp-hours. The typical car, when everything off and parked, drains the battery at about 50 mA. So in 20 hours it would drain 50 x 20 = 1000 mA-hour = 1 amp-hour of charge from the battery. That would imply you could park the typical car with a typical car battery for a little less than 30 days before the battery would be completely discharged.

About charging a dead battery. Batteries have an internal resistance, and it goes way up when it is totally dead. That’s why it is hard to re-charge a completely dead battery. The resistance won’t allow much charging current to flow. It can be done, but not very quickly with the typical battery charger for DIY’ers you buy at Sears. It might take several days of charging, possibly longer than that. The DIY battery chargers don’t put out enough voltage to overcome the charge rate limit imposed by the battery internal resistance.

Any starting battery that sits for an extended period of time sulfates. It doesn’t matter if it sits on the shelf or in a vehicle. And unless you have a pulse charger the battery won’t take a charge.

So if you’re trying to jump start the vehicle that has the dead battery, from what battery/vehicle is the vehicle getting the jump start from?


Thank you, all!
So, it seems like there’s a good chance you could find something if you tried enough cars, then.

cigroller- Thanks for all of that, good points.

Bluegill- I like the keychain idea! Ha!

PvtPublic- Marine batteries, also a good plan.

Barkydog- Thanks for your experience with your battery. I was reading about trickle chargers today–maybe they need one for the future. I do have some characters replacing a battery, but a different character is on foot in a rural area and doesn’t have access to a fresh one.

NYBo- Great idea, thanks! And, yes, they will eventually run into the gasoline issue.

jtsanders- Zombies may walk, but the old rules still apply!

I appreciate you writing that out, GeorgesanJose. That was very interesting and good info to keep in mind.

Tester- The character who’s dealing with this has nothing with which to jump start. That’s why I was curious about the chances of finding a car that would work–with no access to new batteries or a jump. Other characters have had a car since the story began, so they’d use that to jump start.


Then you could jump start the dead battery from the good battery to start the vehicle. But if the battery is sulfated on the dead battery, the engine will stall as soon as the jumper cables are removed.


Perhaps a look-see into the websites of battery manufacturers would yield some sort of expected lifespan curve.

When you want facts, it’s best to go directly to the technical experts. The battery manufacturers are the technical experts. Their websites will have the technical facts.

Maybe stumbling across a car whose owner had left it hooked up to a solar trickle charger?

George, come on, man . . .

There are many of us here who straight out said we have cars that sit for months at a time without being started. Yet they start just fine, without a boost or a charge

I understand how you arrived at that figure, but I know from personal experience that good batteries can start an engine after much longer than 30 days

If they ran across a golf cart, it would have 6 six-volt deep cycle batteries and they would probably hold a charge longer than a car battery. If they found an old garage that just happened to have a truck from the 50"s that had been preserved, then they could jump it with the golf cart batteries and even if the truck battery was sulfated, it would still run because of the generator.

One place that you might find an old truck and a golf cart would be an old nursery. The golf cart would have been used to take large plants up to customer’s vehicles and the truck used for delivery to customers sites.

Get an old kick start Harley and you won’t need a battery.