A dead battery is one of the most common reasons your car won’t start.
Your car’s engine needs quite a bit of energy from the battery to start the ignition.
There are several causes that may be draining it if you find that yours is constantly dead.
Learn everything you need to know about how to charge your battery and how to avoid it always dying in the future.
How Long Will It Take a Dead Car Battery to Charge?
It can take anywhere from 1-24 hours for a dead battery to reach a full charge.
The total time is fully dependent on the charge amp of your battery and the mode of charging you choose.
A typical battery can be fully charged in as little as 10 hours, however if you’re looking to charge it just enough to start your engine, that can be accomplished in as little as 2.
Jump starting the battery will allow you to start the engine, but will not charge the battery instantly.
Does idling a car charge the battery?
Yes, idling a car’s engine will charge the battery.
Anytime the engine is running, the battery will be receiving a charge – assuming the alternator and charing system is all in good working order.
However, simply idling your car may not be the most efficient way to charge your battery up again. Learn more about that below.
Does driving charge a battery faster than idling?
Since the battery gets charged when the engine is running while idling, it stands to reasons that driving around will charge it too.
In fact, driving around will allow you to charge the battery much faster than letting it sit an idle.
However, your car’s battery can die while driving. In that case, there may be other issues you’ll need to address.
Options for Charging a Car’s Battery
The most common options for recharging your car’s battery are idling, driving, or using a charger.
The easiest of those is idling the car or driving around, since they requires no equipment. But, if the battery is completely dead, using a charger may be your only choice.
Your car’s battery will get charged anytime the engine is running.
To recharge your car battery through idling, you’ll need to start your car on and let it sit with the engine running for several hours.
IMPORTANT: You should make sure any electrical function of the car that requires energy is turned off: lights, the radio, AC. This will allow the majority of energy produced by the engine to go back into the battery rather than getting used to power other electronics.
Several hours to let your car sit is a long time, though. So charging the battery by idling, while simple, is probably the least efficient option.
For one, you’ll be wasting fuel and wearing down the engine’s oil unnecessarily.
Next, if you do chose this method, you need to make sure that you are only running your vehicle in a well ventilated area. NEVER IDLE A CAR IN A CLOSED GARAGE.
Driving the Car
Driving your car is the normal method and simplest way in which the battery gets charged.
As your engine runs, the alternator generates power from the rotation of the crankshaft. This current is then converted and regulated to an electrical current that will charge your battery.
Starting the engine draws a significant amount of power from the battery, so if you’re only driving for short trips, it may not be getting charged fully each time you drive your car.
In order to sufficiently charge the battery while driving, you’ll generally need to drive the car for around 30 minutes at highway speeds.
The higher the engine’s RPMs, the faster it spins, and the more energy it produces.
The exact time and distance to reach a full charge through driving will depend on the initial charge of the battery and the speed limits for the roads you’re driving on.
Using a Battery Charger
If letting your car idle for several hours or driving around isn’t ideal, you can buy a charger.
Generally, the cost of these can range from $20-$100 and can be purchased either online or at an auto store.
There are two main rules that you need to follow when purchasing a charger to avoid permanently damaging your battery.
- IMPORTANT RULE #1: Buy a charger that matches your battery’s chemistry. A lead acid battery needs a lead acid charger, an AGM battery needs an AGM compatible charger, and so on.
- IMPORTANT RULE #2: Buy a charger with a matching voltage output to your battery. For example, a 12 volt battery needs a 12 volt charger.
Types of Chargers
There are three different types of chargers that you can use:
- Linear charger.
- Multi-stage charger.
- Trickle charger.
Each of them has pros and cons, which we’ll cover below.
When it comes to car battery chargers, a linear battery charger is the most straight forward option you can get.
A linear charger allows you to charge your battery by plugging it into a wall socket and requires very little set up.
It’s easy to use and can usually be found for relatively cheap.
However, because this charger runs at a low amperage, it takes a long time to charge your battery (up to 12 hours or more).
Another drawback is that the charge is continuous with no controller to stop the charge once the battery is full.
If left unattended and unmonitored, it can overcharge the battery and damaged it permanently.
A multi-stage battery charger sends bursts of power rather than one continuous charge.
This type of charging is typically better for your battery and it removes the potential error of damaging it through overcharging.
It is a lot quicker than a linear charger (you can recharge your battery in as little as an hour).
A trickle charger or battery tender is good to use to prevent the problem of your car battery dying.
This type of charge sends a low, trickle charge to the battery over a longer period of time. With built-in sensors, it can safely be left hooked up without the risk of overcharging your battery.
It is most commonly used to charge cars that don’t get used throughout the winter.
Just know that the power output is very low. It is not the best option to charge your battery if it is dead or if you need a quick charge.
Can you leave a battery charger on overnight?
Before you leave your battery charger hooked up overnight, you’ll want to check which type you have.
Some battery chargers have built-in sensors and cut-offs to prevent a car’s battery from receiving too much charge. These types are safe to use overnight.
Other types of chargers must be monitored so that they do not overcharge the battery. Chargers without a built in cut-off SHOULD NOT be left hooked up overnight.
Jump Start vs. Battery Chargers
For long-term battery maintenance, charging your car’s battery is the best solution.
However, if you’re looking for a quick fix in an emergency, jump-starting your battery is a good choice.
Jump-starting allows you to use another (charged) vehicle to boost your engine’s dead battery using two jump leads.
You’ll simply need a pair or jumper cables and a car with a healthy battery.
Once you get your car started, you can charge the battery by running the engine.
DON’T FORGET: Jump-starting will give your battery enough power to start your engine, but it will not fully charge it.
If you want to continue to charge the battery after a jump start, you’ll need to leave the car running, or better yet, start to drive it.
Will idling the car or driving short distances keep the battery properly charged?
You may be tempted to idle your car for a short amount of time or drive it short distances to keep your battery charged, however this is actually doing more harm than good.
Starting your car takes 100-300 amps and idling it for 20 minutes only replaces about 4 amps. In other words, your battery is never getting fully charged if you just start it and idle for a little bit.
To successfully maintain your car’s battery, you’ll typically need to drive the car for at least 30 minutes, covering at least 10 miles at 30-40 miles per hour.
Common Reasons Why Your Car’s Battery Keeps Dying
If your car battery is several years old, there’s no wonder why it keeps dying. All batteries wear out over time. Most batteries will last you for about 3-5 years depending on usage and other conditions.
However, if your battery is new and it keeps dying, there are a few common causes.
1. You accidentally left the lights on.
Repeatedly leaving on any kind of light in your car will repeatedly cause the battery to die.
An obvious light that could have been left on is your headlights.
A less obvious light to check for is any kind of interior light that could have stayed lit due to the trunk or a door not being closed all the way.
2. You take a lot of short trips.
When you’re consistently taking short trips in your car (less than 10 miles), your battery isn’t getting fully charged.
The best (and healthiest) remedy for this is to start walking or biking when trips only cover short distances.
You can also intentionally take longer trips in your car each time you take it out.
3. Your car experiences extreme temperatures.
If your car experiences extreme temperatures, like a sudden rise in heat or drop to a low temperature, this can cause it to die because it will take longer to charge.
Harsh winter climates and hot desert temperatures can make life hard for your car’s battery.
4. Your car has parasitic drains in the electric system.
Mild parasitic drains are normal.
These are caused by tiny amounts of power to your car’s clocks, alarms, and radio while your car is turned off.
However, if this is causing your car to die repeatedly, there is likely a problem with your car’s electrical system.
This could be caused by a short, blown fuse, too many devices on the same circuit, or too heavy a load somewhere in the wiring.
5. There’s a problem with your car’s charging system.
Your car’s battery fires up the system, but once running, it relies on the alternator to stay charged.
If there’s a problem with your alternator, your battery isn’t going to be charged effectively.
You will likely experience trouble with starting your car even after it was just running.
6. Your car’s battery cables are loose or corroded.
Even if the charging system is functioning properly, your battery will die if the connection point is compromised.
This commonly happens when your car’s battery cables are loose or the battery terminals are corroded.
Shorts or bad ground connections may be another culprit.
If you can’t find a simple solution, and your battery continues to die under normal operation or after using a charger, it’s best to take it to a mechanic for further inspection.