Lithium batteries are everywhere. They are carried by consumer electronic devices such as mobile phones, tablets and laptops. They are carried by tools such as drills, sanders or electric pruning shears. And, of course, they are present in electric cars. A relatively common belief is that electric car batteries will last the same as that of a mobile phone, but nothing could be further from the truth: Electric car batteries work very differently with the aim of last longer.
We are relatively accustomed to the mobile battery lasting two or three years in good condition. If you are very careful, it may last a little longer, but it will still have lost a good part of its original capacity. It’s no secret that Lithium-ion batteries, by their very nature, lose energy capacity with the passage of time. That is, as they are discharged and reloaded and they add charge cycles.
One of the most widespread misinformation regarding the electric car has to do with the useful life of the batteries. To feed this misinformation, there are those who compare them to the batteries of a mobile phone. But electric car batteries are made to last much longer. It is evident that a product costing many thousands of euros, such as an electric car, cannot be designed with a useful life of two years in mind. People would never assume that expense. However, consumer electronics is different.
In order for the batteries to last longer, they have a series of elements and systems that differentiate them very noticeably from those you carry in your pocket. One of the most important is the BMS, or Battery Management Systembut he is not the only one. Let’s look at them in more detail.
More advanced thermal management
On a mobile or tablet, thermal management is very basic. They normally rely on passive heat dissipation, which is why they heat up easily during charging or with intensive use of the device. High temperatures increase degradation.
Electric cars incorporate sophisticated thermal management systems using forced air or liquid cooling. Most modern batteries rely on liquid cooling. This allows keep the battery in an optimal temperature rangegenerally between 20 °C and 40 °C. This prevents overheating during fast charging or heavy use, and also protects against extremely low temperatures.
Controlled discharge depth
In mobile phones and laptops, batteries typically operate close to their theoretical charge and discharge limits to maximize usage time per charge. They are small batteries, so they are used as much as possible, which causes faster degradation.
However, the battery of an electric car has an energy reserve both above and below, which is often called buffer. That is to say, Manufacturers limit the amount of usable battery power to prevent the cells from being fully discharged or charged, which reduces chemical stress of the battery.
That is why we usually talk about gross or installed capacity and net or usable capacity. For example, a Peugeot E-308 has a 54 kWh battery, but only 51 kWh can be used. 5.6% is reserved. The Mercedes EQS battery has 120 kWh installed, of which it uses 108.4 kWh. The German model reserves 9.7%.
This means that even if you charge it up to 100%, it is not actually charged to its maximum thanks to a software limitation. The same goes for downloading. This way, the battery is never fully charged or drainedeven if the car gauge shows 100% or 0% on the screen. Still, many manufacturers recommend keeping the state of charge between 20 and 80 percent.
Less intensive charging cycles
Related to the above, another factor (in this case more typical of the type of use than the design itself) has to do with the number of charging cycles. Normally, the battery of an electric car is not stressed every day. There will be exceptional cases where the user travels many kilometers daily, but generally a low percentage of the battery is used each day. This reduces the number of complete charge cycles carried out throughout the year (and therefore, its entire useful life).
On the other hand, it is rare that we do not charge our mobile daily. Whether due to very intensive use or somewhat poor autonomy, we are plugged in (in various ways) to the mobile phone every day. This means more charging cycles in a shorter period of time. In addition, cell phones are often charged even while in use, generating additional heat. And as we have seen before, more heat means faster degradation.
Cars put greater emphasis on durability with stronger cells
What is better? Have more autonomy or have a battery that lasts longer? The ideal would be to have both, but you have to find a balance… Or adapt to the needs of each product. In a small device such as a mobile phone or a laptop, the battery cells are designed to be compact, light and with the greatest possible autonomy, prioritizing energy density over durability, since these devices are generally expected to have a life cycle of just 3-4 years.
For its part, Electric cars use cells with a more stable chemistry and resistant to chemical aging with the aim of lasting longer. More and more manufacturers are opting for lithium-ferrophosphate (LFP) batteries, which have significantly greater durability, supporting 5,000 charge cycles and even more with minimal loss of capacity. LFP batteries have lower energy density, making them unviable for small devices.
While a cell phone battery can drop below 80 percent of its original capacity in just a couple of years if used intensively, car manufacturers typically give warranties that cover 70-80% of the original capacity for 8 -10 years or 150,000-300,000 km, depending on the manufacturer.
BMS, the brain that is responsible for monitoring everything about the battery
There is a component in electric cars, which mobile phones do not have, that is responsible for controlling the temperature in the battery, supervising charges and discharges, controlling the voltage and current in each cell… It is the BMS, acronym for Battery Management Systemeither Battery Management System. It is what makes the difference and the system in charge of controlling many of the things that we have mentioned in previous paragraphs.
He BMS It is one of the most important components of an electric car. It is in charge of monitor, analyze and protect the vehicle battery to guarantee its operation in the most efficient and safe way. In addition to improving security, it is vital to increase battery life.
The BMS is an electronic system that Continuously monitor parameters such as voltage, current, temperature and state of charge through multiple sensors and a control unit. This is responsible for analyzing the data collected by the sensors, making decisions and sending signals to other systems in the car, such as the inverter or the driver’s screen.
Since cells do not always discharge or charge evenly, the BMS is also responsible for leveling their state of charge. The BMS has a cell balancing systemwhich serves to all cells work equally and a few are not punished excessively, prolonging their useful life. Through passive balancing, the most charged cells dissipate excess energy in the form of heat to equalize them with the others. Active balancing transfers electrical energy from more charged cells to less charged cells, maximizing efficiency.
The BMS also controls the amount of energy that enters the cells during charging, optimizing fast charging without overloading. In the event of overvoltage, overheating or short circuit, the BMS can cut off power, reduce vehicle power or disconnect the battery from the charging system.
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