People often wonder if there is some kind of a car battery other than a standard lead-acid one. The main thing you might asking this is because you want to know why car batteries are so heavy.
Let’s clarify some things first, and then take a look at five popular types and their weight:
Why car battery is heavy?
The main reason why car batteries are heavy is because the main component insinde the battery is lead. There is a lot of lead inside of the car battery, and lead is very heavy by nature. This technology has been used for over a hundred years now. It will not be replaced any time soon, it will only get better.
What materials are car batteries made of?
When we think of car batteries, we really think of lead-acid ones.
But, there are several battery types of which are standard flooded lead-acid, deep cycle, Marine batteries, AGM, and Lithium Iron Phosphate batteries.
There’s a four main component that makes a battery.
The casing is made out of sturdy and durable plastic materials. It has to be durable to withstand various conditions, and also it needs to be resistant to acid inside the battery.
The second components are terminals and metal plates.
They are made out of the lead. The positive plates are made of lead oxides in numerous compositions, and the negative plates are made out of the metallic lead.
The lead is very heavy, and in the same time is too soft so it can’t support itself.
Because it’s a soft material, terminals might melt if you don’t take care of them. Check here to see what are the main causes terminals getting hot.
Small quantities of calcium, tin, antimony, selenium are added to get the mechanical strength and to improve electrical conductivities.
The third component is the plate separator.
Depending on the battery type, several materials are used to build separators for plates, including rubber, glass fiber mat, cellulose, and PVC or polyethylene plastic.
The separator needs to be a bit larger than plates to prevent a short circuit.
The fourth component is the electrolyte. The lead plates are submerged in an electrolyte solution, typically made of 35% sulfuric acid (H2SO4) and 65% water.
Car battery types
Lead-acid batteries are a very popular choice for vehicles and in many other applications too.
For different applications, batteries need to stay relevant to the job they have.
Because of that, more types are made.
Popular types are:
- Lead-acid
- Deep-cycle
- Marine battery
- Absorbent Glass Mat (AMG)
- Lithium Iron Phosphate (LiFePo4)
All of these types of batteries are very heavy, except the last one. Lithium Iron Phosphate is substantially lighter because it does not contain lead as cathode and anode.
All of them are rechargeable, so they can be reused on a daily basis.
Lead-acid batteries
Lead-acid batteries as the name implies, are made of lead. Because their plates are made of lead these batteries are very heavy.
They are also very popular in the automotive industry because they are inexpensive on a cost-per-watt basis. And also, they are able to supply high surge currents. That means the cells have a very large power-to-weight ratio.
So, lead-acid batteries can provide the high current required by the starter motor. They are also called starter batteries.
All the car battery manufacturers make lead-acid batteries for all of the brands out there. Comparing lead-acid battery brands by looking at specifications you can’t tell any difference. You really must know the quality of what’s inside.
A regular car battery contains six cells with 2 Volts each. Combining cells together in series, we get 12 Volts output.
The average weight of a lead-acid battery is 39 lbs (17 kg).
Deep-Cycle batteries
A true deep-cycle battery is designed in a way that can be discharged 80% without causing any damage.
The difference between deep-cycle and lead-acid batteries is that deep-cycle have much thicker lead plates, and they are as much as three times heavier than lead-acid once.
The average weight of a deep-cycle battery is about 70 lbs (32 kg).
Because they can hold power much longer and can be discharged deeper, they are pretty commonly used as backup power and also in solar-powered plants.
These batteries can not be used as starters to start vehicles such as cars or trucks.
Marine Battery
Marine batteries are real hybrids. They are designed to bring the best properties from both lead-acid and deep-cycle batteries.
Because they have a dual purpose, they are the best solution for boats. That’s why they are called Marine batteries.
They can be used to start an engine as well as to be deeply discharged without damage.
Marine batteries do not have thick plates as the deep cycle does. It has a style of plates like lead-acid does with a difference that marine batteries have stronger and heavier plates.
The average weight of a marine battery is about 60 lbs (27 kg).
Often, people use marine and deep-cycle terms interchangeably which is partially true.
Marine batteries are deep cycle, but true deep cycle batteries are not marine batteries.
Absorbent Glass Mat (AGM)
AGM are a type of lead-acid battery but with superior properties.
Compared to lead-acid batteries, they are extremely resistant to vibrations, and they are completely maintenance-free.
AGM technology stands for a separator that is being used between plates.
This separator absorbs all the acid electrolytes that can not be spilled.
It’s a completely sealed system but for safety reasons have vents in case of extreme overcharge.
AGM batteries are made in a way when a certain threshold of internal pressure is not reached, cooled down gas will not vent out of the battery but rather combine again with the solution inside the Absorbent Glass Mat separator.
AGM batteries can be recharged five times faster and they can last three times longer than lead-acid.
They are used in applications with a high power demand such as start-stop systems.
AGM batteries use plates made of 99.99% lead. A positive and negative plate with an AGM separator between them is tightly compressed together inside each cell and held under pressure inside a plastic casing.
This will ensure lower resistance and better flow of electrons.
Their weight is about the same as a regular lead-acid battery.
Lithium Iron Phosphate (LiFePo4)
Unlike other lead-acid batteries Lithium Iron Phosphate is not made out of the lead and sulfuric acid.
LiFePo4 is way lighter comparing to any other counterpart lead-acid battery types. Its weight is about 26.4 lbs (11.98 kg).
Lithium Iron Phosphate or lithium ferrophosphate is a type of lithium-ion battery that for its cathode use LiFePo4, and for its anode use graphitic carbon electrode with a metallic backing.
The main reason LiFePo4 is more costly upfront is because they are much more advanced than lead-acid batteries.
It delivers two to three times more of the amount of power out of the same size counterpart lead-acid battery.
Even they cost much more upfront it’s much cheaper in the long run. It can cycle over 5000 times. So, per cycle, LiFePo4 is much more affordable than lead-acid.
It also eliminates maintenance in terms that you don’t need to clean terminals and worry about off-gassing. Terminals will not corrode.
Because regular car batteries still use acid as electrolyte, off-gassing make terminals to corrode. Check here to see why it’s very important to use grease on battery terminals to prevent corrosion.
Is a heavier battery better?
Heavier batteries are energy denser than batteries made out of the same material but lighter.
If you have to store a lot of energy, the answer is clear, you need a heavy one. But, if you need to save weight, you must compromise between the energy you need and weight.
Let’s take a look at some examples:
If you live in a house with an off-grid system the weight is not a concern. You will use very heavy batteries in order to store as much power as you can get.
When Sun goes down power from batteries kicks in. You don’t want to lose power when it’s night.
For a regular vehicle you will use battery specs by the factory. To be on the safe side, you can use a slightly larger and heavier battery, that’s not a problem at all. If it fits inside the battery compartment then it’s ok.
If you’re a race driver saving weight is a must. Basically, racing vehicles must be as light as they can get because lighter is faster, right? Because racing cars will use batteries only for starting you can use a slightly smaller and lighter battery to stay lightweight.
As you can see from these examples, lighter or heavier batteries are a better choice depending on the case.
Do batteries weigh less when dead?
Opinions are divided here.
But, if we use scientific formulas and ways to measure things then the answer is yes, the weight is different.
You can try it yourself. Use any battery and measure it when it’s charged all the way up and measure it when it’s discharged all the way down.
You will understand that there is no way to see a difference in battery weight with our scales at home.
The battery will be the same weight before and after the measurements.
Particularly when it’s a closed system, there is no way for electrolyte vapors to escape.
But, if we watch lead-acid batteries, then measurements may differ because the acid will escape little by little over time, and the battery will weigh less.
This is not a direct answer to the question because the battery will weigh less, either being charged or discharged.
Why car batteries are still so heavy?
Car batteries are made out of the lead, and lead is heavy metal in terms of weight.
Lead-acid batteries became common in cars in 1920. As you can calculate it is a very long period, and we still use the same technology.
They are cheap to produce and very efficient and powerful.
So, why change them when they work just fine?
We still use concrete, asphalt for roads, steel for buildings and bridges, right? And these are just a few examples, and we take them for granted.
Although the principle of operation is the same, lead-acid batteries are advancing and improving their performance.
Yes, although they are progressing, they are still heavy because of the lead inside of them.
New technologies such as LiFePo4 allow us to use lighter batteries in our vehicles.
Because LiFePo4 is more advanced than lead-acid it’s expensive up front. So, a small amount of people decides to use them as the main choice.
If manufacturers continue to make batteries with lead, it will stay heavy till something else come into its place, perhaps some lightweight material.
Comparison table
| Car Battery | Weight (average) |
| Lead-acid battery | 39lbs (17kg) |
| Deep Cycle battery | 70lbs (32kg) |
| Marine battery | 60lbs (27kg) |
| Absorbent Glass Mat (AGM) | 39lbs (17kg) |
| Lithium Iron Phosphate (LiFePo4) | 26.4lbs (11.98kg) |
Helpful Sources
Read this pdf document to understand car batteries construction, and more useful informations about them.