How Tesla Batteries Work

‍Gas Power vs. Battery Power

Fundamentally, batteries are just another way to store energy. Electric cars use batteries, which are charged by the grid, to store power for use on the road. Gasoline-powered cars store fuel, which is not the same principle.

The fuel itself stores combustion energy, which is released when ignited. Batteries, on the other hand, have to be ‘filled with energy itself—not just a medium that already has energy such as fuel.

This is why gasoline is so fast and convenient in comparison. The fuel already has energy stored in it, so all you have to do is move it with a pump. Batteries take time to charge, as energy flows into batteries far slower than liquid flows into a tank.

Gasoline also stores much more energy per pound than batteries do, as batteries are complex systems with limited energy capacity. As a result, batteries in an electric car weigh far more than a fuel tank full of refined petroleum with equal energy output.

So far, we’ve discussed the benefits of gasoline power. And from an energy storage standpoint, gasoline is far superior to batteries. But that doesn’t tell the whole story, as you have to convert that energy to something useful.

Gasoline cars use engines to convert stored gasoline energy to useful mechanical motion. Engines are complex and extremely inefficient, as much of the stored energy is lost in the form of heat. On average, modern gasoline engines only utilize 35% of the energy stored in gasoline usefully.

This is where electric cars begin to shine. Sure, even high-tech Tesla batteries lose some energy due to heat. That number is far lower than gasoline engines, as Tesla batteries utilize 75.2% of energy usefully. That means that mile per mile, Tesla batteries are a far better use of energy.

What Makes Up a Tesla Battery?

A Tesla automotive battery isn’t a single battery cell. In fact, it’s made up of thousands of individual small battery cells which are wired together. A more accurate way to describe it is a battery bank.

The batteries used in the battery bank are of the lithium-ion variety, which is the same kind of battery found in most phones and laptops. Lithium-ion batteries are relatively efficient and reliable, and they store an enormous amount of energy for their size.

Lithium-ion batteries are somewhat volatile, but they’re still a dramatically superior alternative to other battery types. They’re also lightweight, which is critical for car design. It would only take a few small lithium-ion batteries to store the same amount of energy found in a 30-pound lead-acid battery.

Contrary to popular belief, lithium-ion batteries don’t have a ‘memory effect. The memory effect is a phenomenon that occurs with some kinds of batteries that leads to inconsistent charging and loss of charge potential from improper use.

Tesla 18650 Lithium-Ion Batteries

The first renditions of Tesla’s battery packs utilized thousands of 18650 cells. These are common consumer batteries, and they’re found in a wide range of products. Other uses for 18650 batteries include speakers, mobile phone charging packs, laptop battery packs, heavy-duty flashlights, and other electronic devices.

The 18650 batteries used by Tesla have a capacity of 3400 mAh. They measure 18 mm across and 65 mm long. These batteries have a nominal voltage of 3.8 volts and a range of 3.3 to 4.2 volts, and a 17 amp maximum discharge current. Individually, they have enough energy to charge a cell phone a few times.

Tesla 18650 batteries are made by Panasonic, and their quality is extremely high. As a result, these pricy cells are more stable, safe, and reliable than cheaper alternatives. It may seem odd to spend so much on batteries, but Tesla’s decision to buy the good stuff is completely justified.

Quality is extremely important with Li-Ion batteries, as cheap copies have a tendency to randomly catch fire or burst. One manufacturer of low-quality 18650 batteries once boasted that “only one in 1,000 of (his) batteries explode,” which is why it’s worth paying more for better batteries.

So, in short, Tesla 18650 batteries are the best in the business and extremely safe. They’re reliable and store enough energy to power all of the systems in the car, including heat and air conditioning.

Tesla 2170 Lithium-Ion Batteries

Tesla recently transitioned to the slightly larger 2170 cell for its battery packs. This lithium-ion battery is functionally identical to the standard 18650 cells, but it’s more efficient and manufactured at Tesla’s new Gigafactory. In-house battery production has long been a goal for Tesla, as it gives them more control over prices and quality.

The Tesla 2170 cell measures 21 mm across and 70 mm in length, making it roughly 15% larger than the 18650 cells. As you’ll notice, the name of the batteries denotes their dimensions in millimeters. The 2170 cell weighs about 70 grams and is rated at 4800 mAh. It produces a nominal voltage of 3.7 volts, with a range between 4.2 volts and 2.5 volts.

Tesla 4680 Lithium-Ion Batteries

Tesla uses different, much larger batteries for its Model Y battery packs. The 4680 battery is a large lithium-ion cell, and it benefits from reduced cost per kWh to produce. The 4680 battery measures 46 mm across and 80 mm in length and has a capacity of 5,000 mAh. The Tesla 4680 battery dwarfs the 18650 and 2170 in every measurable way, though the mAh capacity isn’t a huge improvement over 2170 batteries.

Understanding Tesla Battery Charge and Discharge Voltages

Nominal voltage is the number used to assign a class to a battery. You can think of it as the average of the battery's working voltages. The actual charge and discharge rates vary and are measured as peaks and minimums.

The minimum rate defines how low a battery will discharge voltage. In the case of the new 2170 cell, the minimum voltage is 2.5 volts. The maximum voltage indicates the highest charge voltage that the battery will accept. In the case of the 2170 cell, it is 4.2 volts.

Why did Tesla Switch to 2170 Cells for its Batteries?

Tesla switched to the 2170 cell because it’s larger and more efficient. Additionally, it works better for vehicle applications. Initially, Tesla was financially and technically restrained from manufacturing the best battery types for its cars. Instead, it chose the 18650, which was a reliable and commonly available option.

Now, with increased capital and demand, Tesla has the money and expertise to manufacture the most ideal version of lithium-ion batteries at an acceptable price. At this time, the 2170 fit the bill perfectly and is now standard. Total, the energy density increase from the upgrade is 20%, which provides extended range and reduced downtime.

How Many Cells are in a Tesla Battery Pack?

The amount of individual lithium-ion cells in a Tesla battery pack varies between models. Tesla’s most common 18650-based battery packs contain 7,104 individual cells. Total, these combined cells produce around 85 kWh of energy.

The newer 2170 cells are larger and more efficient, and the packs are designed differently. With a similar number of cells, the new 2170 packs produce about 100 kWh of electricity.

Charging Tesla Battery Packs

Tesla batteries can be charged at home or on the road, with varying rates of charge depending on the system used. Teslas can also be charged at generic electric car charging stations with the use of an adapter.

Charging at Home

Tesla batteries can be charged using a home outlet, a public charger, or a wall connector. The slowest and easiest way to charge a Tesla is with the Mobile Connector. You can plug it into a standard 120-volt home outlet without any modification or installation. This method adds about 2 or 3 miles of range per hour, which is quite slow.

If you’re looking for a slightly faster charge, you can use Tesla’s 240-volt adapter and plug it into an industrial outlet in your garage. This is still slower than the wall plug, but not by much—a 240-volt outlet will add 30 miles of range per hour, which is significantly more than the 120-volt outlet.

Tesla wall chargers are the fastest way to charge a Tesla battery at home. These chargers, when installed by a certified Tesla technician, charge the batteries at a rate of 44 miles of range per hour.

Charging on the Road

Tesla Superchargers are the fastest way to charge the batteries on the road. They can charge at an astounding rate of 200 miles per 15 minutes of charging, which is amazing compared to the home trickle chargers. Third-party charging stations vary widely in charge rate, but most can be used with the additional charging adapters.