There’s nothing worse than getting in your car on a cold morning, only to realize that your battery is dead! This is particularly annoying if you’ve had to jump it multiple times, and the mechanic insists that the battery is tested fine.
You probably want to throw it away and just buy a new one. DON’T! One of the main reasons for repeated jump starts is that the battery was never fully charged after it died.
Which brings us to “how long does it take to charge a car battery?”, keep reading to find out.
How long does it take to charge a dead battery?
Depending on the battery type and charging mode, it can take anywhere from an hour to a day to charge a flat car battery, perhaps longer.
Four things to remember about charging a car battery:
- To fully charge a typical car battery with anywhere from 4-8 charge amps or more, it takes approximately 10-24 hours.
- To give your battery enough boost to start the engine, it’ll take about 2-4 hours.
- The optimal way to prolong your car battery is to recharge it slowly.
- You can recharge your battery faster and more aggressively, but it can hurt the long-term performance of your car battery.
How Many Amps Is Your Battery?
No, we are not talking about cold-cranking amps. We are talking about how long your battery can put out One Amp of power (without charging). Most automotive batteries are 48 amps.
While your car does not use an amp per hour, this is the best way to know how long it will take your battery to charge.
That is because the manufacturers make battery chargers this way, so it makes it easy to answer the question of how long to charge a car battery.
If you charge your completely dead battery (0 amps) with a 1 amp charger, it will take you 48 hours, and if you charge it with a 2 amp charger, 24 hours.
Each amp that the manufacturer rates the charger gives back one amp to the battery per hour.
It is also important to know that this depends on the battery as well. If you have a bad cell or a battery that cannot hold a charge (due to calcification), you may have to leave it on the charger much longer to have any chance of even bringing it back.
How Dead is your Battery?
Not all dead batteries are the same. A battery that tests 2 volts would require longer charge time than a battery that tests 10 volts.
Your volts do not necessarily indicate how many amps are left in the battery but it is the easiest to check and essentially lets you know whether it needs to be on the charger longer.
Do not rely solely on the battery light on the dash; it may or may not come on (depending on how low the battery is).
If your battery never completely recovered to health, then it’s a wonder that it keeps dying on you.
Voltage Doesn’t Matter… But it does
A car does not start on voltage; it starts on amps. But if your battery has low voltage, it means it has low amps and you need to get it charged.
The simple way to break it down is if your battery has less voltage, it has less amps; however, just because a battery has full voltage does not mean it has full amps.
For charging purposes, this doesn’t really matter – if it comes up full and wont start your car, then it has a defect and needs to be replaced (but if you charge and it does have low voltage, it does not guarantee that it will start your car charged).
How Long Does the Alternator Take to Charge a Car Battery?
If you’ve ever had a mechanic jumpstart your car, they’ve likely told you to let it run for a little while before you turn it back off. This allows the alternator to charge unless you’re OK with the prospect of a dead battery again as soon as you turn the car off.
However, what is a “little while,” and when is it safe to turn your car back off? The answer to how long you should charge the car battery using the alternator is not so clear-cut.
The charging time depends on how fast you’re driving your vehicle. Your alternator is belt-driven, and the RPM of your engine affects the belt speed.
When you drive faster, your alternator can work harder. If you are driving on the interstate, your alternator can generally get your battery back to life within 30 minutes, but if you are sitting still in the driveway, it may take longer, like a few hours, to get the charge back to full.
You should also note, that when your alternator is charging your car battery, it’s like a 40-amp charger because it’s giving the battery power as fast as it can dump it into the battery. This is effective, but it exhausts battery life sooner.
Fortunately, the alternator behaves like a smart charger. As soon as your car battery reaches the correct voltage, it starts dumping excess voltage to ground, so you don’t have to worry about overcharging your battery!
Types of Car Battery Chargers
40-amp Chargers
40-amp chargers (often called 200-amp, as it refers to jump starting) are the fastest ways to charge a battery, but there are some risks associated with their use.
The biggest risk is that you leave the charger on too long and overcharge the battery. This will ruin the battery and if you did it for long enough, you might even cause the battery to explode!
Furthermore, charging anything other than a trickle charge can damage a battery and will decrease its performance capacity and lifecycle timeframe.
This damage is of little concern if you are only charging your battery once, and you successfully get it off the charger before the damage happens. However, if you subject your battery charger to this repeated use, it can be significant.
Trickle Chargers
Trickle chargers typically come in two different amp sizes – 1-amp chargers and 2-amp chargers.
2-amp chargers will give you some benefits over a 1-amp charger based on the increased amp rating. The most significant benefit that they provide is that you can charge your battery in half the time.
If you battery is completely dead, it would take a 1-amp trickle charger 48-hours to fully recharge it; with a 2-amp trickle charger, that timeframes is only 24-hours.
While charging your battery will still take a long time, being able to do it in half the time is significantly more efficient.
Additionally, while charging your battery too fast, too frequently may significantly cut your battery’s life span, you can rest assured that with a 2-amp trickle charger, the charge is still slow enough that you do not have to worry about it being damaged.
The major downside to a 2-amp charger over a 1-amp charger is the extra cost. If you are going to use it often, it is worth every penny.
However, if you are going to keep it in your garage because you will use it once or twice out of every year, the 1-amp charger will most likely work satisfactorily for you.
Smart Chargers
If you have concerns about getting your battery off the charger when it is complete and not damaging it, you should consider buying a smart charger. Smart chargers are able to sense the charge of your batteries and adjust the charging volt with regard to how charged your battery is.
Manufacturers make both 40-amp chargers and trickle chargers with smart charger technology, which is part of the reason why we strongly recommend the investment for the little extra money.
The prices may be marginally higher than regular chargers, but if it can save you one or two batteries from being overcharged, you have covered the extra cost of this type of charger.
If fact, smart chargers allow you to safely go work on other areas of the vehicle that may require maintenance and not have to sit there and watch the charger.
With the charger’s power output being automatically adjusted, there are fewer chances of a fire or explosion risk than with regular chargers.
Pros and Cons of Trickle Charging
If you can afford the time, trickle chargers are really nice to use because they have many advantages compared to 40-amp chargers. The biggest one being that they are less likely to damage your battery and will usually preserve its lifespan as well.
While a 40-amp charger can charge most batteries in less than an hour, trickle chargers typically take one or two days to charge a battery. So, if you don’t have the time to wait, you will need something other than a trickle charger.
Pros
- Less likely to damage your battery
- Preserves battery lifespan
- Typically cheaper
Cons
- Is much slower
- Is easier to forget about
How Many Volts in a Fully Charged Car Battery?
Modern cars are generally fitted with a 12-volt battery under the hood. A 12-volt car battery is made up of six cells which each will produce about 2.1 volts of energy when fully charged. When the engine is turned off, a car battery is considered fully charged between 12.4 to 12.6 volts.
A drop in voltage from the normal range to a lower range can impact your battery’s overall performance.
For example, if the voltage drops to 12.1 volts, it means your battery is only charged at about 50% of total charge. If it reaches 11.6 volts, it is almost depleted and losing about 5-6 volts if it continues to be used.
How long take you to drive to Charge Your Car Battery?
The car engine needs to be revolved at a minimum of 1000 revolutions per minute (RPM) to produce enough power to charge the battery. Faster speeds mean faster RPMs, so your battery will charge best and fastest at speeds of 55 MPH or higher.
It takes most vehicles 30 minutes at highway speeds to be fully recharged. Thirty minutes is average; so it could take longer if your battery is deeply discharged.
Related Post: How Long You Have to Drive to Charge Your Car Battery?
Does a Car Battery Charge When Idling?
Your battery will recharge from a car that is idling, but at a much slower rate than when driving the car. The reason for the slow charge is that modern cars have many more electronics that consume power. Guess what component powers those systems? That’s right, the alternator.
So when your car is idling, it is not producing a high RPM meaning the battery will take much longer to charge + hours. The best option is to take the car for a drive instead of idling in your driveway.
How Long Does a Car Battery Last Without Driving?
A car battery will go from fully charged to completely dead with no driving in less than two months. Your battery will take longer to die if it is less than three years old or if you charged it before you parked it. A combination of excessively short trips isn’t good for battery life.
There is nothing wrong with running errands, but if that is mixed with a lot of stops and starts with a small amount of driving done in between, you are going to hurt your battery life.
At minimum, you should be taking 30-minute highway driving sessions once a week so your alternator has time to fully charge your battery! Find more ideas on why your car battery keeps dying
Can I charge my car by jump-starting it?
If your battery died because your alternator isn’t working properly, you may be thinking that you can just leave it hooked up to another vehicle with jumper cables and let it charge up a bit that way.
The short answer is, don’t do it. Yes, it will work, but with all the electronics inside the cars today, leaving your running vehicle hooked up with jumper cables to another vehicle is a disaster waiting to happen.
You could easily short out electronics, which could lead to hundreds of dollars in repairs. It may be a hassle taking a battery out of a vehicle at the location it is in, but it is going to save you hundreds of dollars in repairs.
To finish, if your vehicle does have a bad alternator, please don’t try to drive it to the shop. Your battery is not going to get charged and it will die without power, killing your engine while you are driving.
Instead of getting stranded in a parking lot or your driveway, you are at a high risk of being stranded on the side of the road and having to call a tow truck to get to where you are trying to go.