11 Reasons Why Car Batteries Are So Heavy

Car mechanic replacing the old car battery with a brand new one wearing gloves and pulling out the battery installing a brand new one

I recently swapped out a battery on my old car and was blown away. I always forget how heavy car batteries are until it’s time to change one out. This got me to thinking — why are car batteries so heavy? I did some digging and came up with 11 major reasons why they’re so heavy. I’m going to briefly talk all about battery weight in this article.

It all comes down to the chemistry going on and the required power. Batteries need to work in cold temperatures and can’t take any breaks. As such, designers need to overengineer batteries. That turns into added pounds. Plus, designers are more concerned with reliability and convenience, so the weight isn’t a big focus for them. Since lead-acid batteries use lead, there is an unavoidable weight that is added thanks to this dense material.

How Much Do Car Batteries Weigh?

Let me start by answering a simple question about batteries. How heavy are they really? Well, a typical commuter vehicle will have a 12-volt battery that weighs somewhere between 25 and 55 pounds. The average battery weighs 40 pounds.

40 pound lbs dumbbell against a grey background

As your vehicle gets bigger, sportier, and heavier, the battery will also get heavier.

Why Does the Battery Weight Even Matter?

Your battery weight isn’t incredibly important. I will say, that weight matters when you’re swapping out batteries.

The process involves grabbing your current battery with basically a giant claw. You then need to manually pull the battery straight up and lift it out. Since you’re bending over a car’s hood doing this project, the weight can get really uncomfortable.

The difference between 25 and 55 pounds in this instance is pretty remarkable.

A male mechanic with white gloves carrying a white battery to the vehicle

Beyond that, total weight is going to change your car’s performance. Admittedly, a difference of 25 pounds isn’t going to be really noticeable for the typical driver. Still, it’s worth mentioning.

It’s a bigger deal in high-performance situations. To avoid losing races based on battery weight, Formula 1 actually has a rule. All the cars’ batteries need to weigh between 44 and 55 pounds. For context, that’s a sport where every pound matters, and a win can come down to fractions of a second.

If you want me to simplify the answer to this question, your car battery’s weight doesn’t really matter for the average driver.

This Is for Lead Batteries, Not Lithium-Ion Batteries

Just to quickly clarify, I’m only talking about the batteries used in internal combustion (gas-powered) engines. In electric cars, the batteries would be comparably much lighter if they were the same size. Of course, they have to be massive since they’re responsible for fueling a vehicle for hundreds of miles.

11 Reasons Why Car Batteries Are So Heavy

To get right into it, here are 11 of the biggest reasons why car batteries are so heavy. There’s some overlap between some of the reasons, but I’ve included them all so you can get the full picture.

1. The Number of Internal Cells

Without boring you with the scientific details, there are segments of your battery, called cells. Each of these cells produces a certain amount of power and can only work so fast.

In order to get more power, you have to put a number of these cells together inline. Their created power is then pooled together and used throughout the car.

Inside of a car battery - cut

In a 12-volt battery, there are typically six cells. Each of these cells produces about 2.1 volts, so you get a total of 12.6 volts.

The chemical process and the amount of power needed can’t be changed.

2. The Charge Adds Weight

A fully-charged battery weighs more than a completely depleted battery. In fact, a depleted battery might only weigh 10 or 15 pounds. Compare that to the 30-50 pounds that a charged one weighs, and you can see how heavy the chemical reaction is.

Car battery recharging

That’s because each of these cells has lead and acid that need to react in order to create usable electricity for your car.

3. They’re Built with Convenience in Mind

When a designer is making blueprints, they need to have a design objective in mind. It might be to optimize power, create the most lightweight option possible, or make a convenient product.

In the case of car batteries, convenience is one of the biggest considerations. After all, there are just two terminals that control everything that you need to care about.

If they changed up the configuration of the battery and made more ports and a more inconvenient setup, I’m sure they could cut down the weight — but at what cost?

4. They Are Lead Batteries

I mentioned that these are lead-acid batteries. If you know a little bit about lead, you’ll know just how heavy this material is.

Yes, batteries use real lead inside to create electricity.

How a lithium ion battery works for EV electric vehicle cars and batteries

A cubic inch of lead weighs 0.41 pounds. To give context, a zinc chunk of the same size only weighs 0.26 pounds. Lead is a very dense and heavy material, and it’s unavoidable if you want to make a lead-acid battery.

5. Amperage Requirements are High

I mentioned earlier that there are six cells in your car’s battery. I mentioned that this was due to a voltage requirement.

Well, there’s also an amperage requirement. Amps tell you “how much” electricity can flow through the circuit. A higher amperage means there’s more available electricity for all the components in the circuit.

Inspecting the car battery

In this case, I’m talking about users like your car’s HVAC system, stereo, and lights.

To create more amps, each cell of the battery has to be bigger. Multiply that six times, and you’ll get an even bigger, heavier battery.

6. It Has to Start in the Cold

Amperage is also dependent on the weather. When temperatures drop, so do the available amps generated from a battery.

A person replacing the car battery in the winter with snow

Of course, we can’t all stay home when it gets cold just because automotive batteries stop working. To avoid this, manufacturers have to design the battery to provide even more amps. When it gets cold and the total amperage drops, it will drop to an acceptable level since the designers overdesigned the system.

This is one way to prevent your battery from dying when it gets cold out.

7. Manufacturers Sacrifice Weight for Price

There are certainly better ways to make lightweight batteries. For example, Lithium-ion batteries weigh a lot less. The downside? They also cost a lot less.

If you wanted to truly optimize where cars get their energy from, you’d need a very expensive component.

A mechanic installing the car battery in the back of a Mercedes-Benz lifting it by the handles

Since manufacturers are designing cars for the everyday consumer, they are deciding to focus on lower prices. As a result, batteries are going to be bigger and heavier.

In my opinion, this decision is a no-brainer. I’d happily take a much heavier battery if it means saving thousands (or tens of thousands) of dollars.

8. They Use a Lot of Metal

Since the chemical process is so dangerous, the battery needs to ensure everything is contained. One way to do that is by using a lot of strong metals.

The majority of the battery on the inside is primarily comprised of metal. The exterior skin including the handles is made of plastic.

Car Battery Cells open

Just like lead, metal is generally very heavy. If you compare steel to regular polypropylene plastics, you’ll see a weight difference of more than 7 times. For instance, a plastic piece that weighs 5 pounds would weigh upwards of 35 pounds if it were made out of metal.

Metal is a lot stronger than these lighter-weight options like plastic. It means that things can bang into your battery and it won’t shatter, spilling acid everywhere.

9. They Have to Survive Tough Environments

Speaking of resilience, these batteries need to be prepared to endure tough environments. They get rattled around, struck, rained on, and exposed to freezing temperatures.

A pile of scrap car batteries lithium-ion ready to be recycled

If battery designers only had to worry about making a product that can survive sitting on a table at room temperature without ever being hit, then it would be significantly lighter.

When you start adding all these different environments, you need to make a durable and versatile battery. As such, the battery gets bigger, more powerful, and heavier.

10. They Need to Be Overengineered

The simple way to put it is that these batteries need to be over-engineered. This refers to the fact that they’re in tough environments as well as the constant load put on the batteries. In addition, their amperage is higher than it needs to be.

Young engineers wearing hard hats designing something on a PC computer

They need to be sturdier to survive daily driving.

In this case, overengineering results in a lot of extra material being used and weight added. If the engineers were to take easy alternatives, then the battery would be lighter weight, but it would fail more often.

11. They Are Always Being Used

Another thing to remember is that your battery doesn’t take any days off. There are always components siphoning power away from the battery whenever you’re driving.

Green car battery illustration

If your car’s battery didn’t make electricity quick enough, then different parts of your car would fail. Of course, this isn’t an acceptable design. To avoid that, engineers ensure the battery will always make more energy than it needs to use when working alongside the alternator.

This means that the batteries will be bigger and heavier.

Conclusion

Now you’re a battery expert. I just covered 11 reasons why your car battery is so heavy. Knowing this information won’t save your back next time you pull out a battery, but at least you have a fun conversation starter with your mechanic friends. If you want more of your car questions answered, check out my site or drop a comment below. I also have a list of car products that can save you some effort in the future.

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Ernest Martynyuk

An automotive enthusiast who's been tinkering with vehicles since I was 15-years old. Repairing automotive electronics has been my main job for over a decade now and have a passion for everything technical regarding cars.

6 thoughts on “11 Reasons Why Car Batteries Are So Heavy”

  1. Wow! This was a helpful read. I had to read about it because I’m currently at the workshop changing out my battery and just wondered why they were so damn heavy. Thanks

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    Reply
    • Pickup trucks and European cars have some of the heaviest batteries. Check out my ‘recommended’ page for the battery carrier I recommended.

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  2. It’s interesting that you said that when temperatures drop, so do the available amps from a battery. I want to test my car battery since I fear something is wrong with it because it is quite old. I’ll need to consult with an expert to figure out what’s wrong with my automobile battery. Thank you for writing this!

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    • I would recommend investing in a portable battery tester if you want to save some time by not having to remove it and bring it to an auto store to test whether it’s good or not. Another important thing not to forget is some cars are very sensitive to voltage dips or spikes. This means that a battery might test good but if it’s already more than five years old, it might have a slight degradation which can cause electronics to go crazy. Something to keep in mind.

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