Electric vehicles (EVs) are rapidly growing in popularity as an eco-friendly alternative to gas-powered cars. Though EVs don't have traditional internal combustion engines, they still require a standard 12-volt lead-acid battery to power auxiliary systems. This seems counterintuitive for a vehicle that is supposed to be environmentally friendly. Why do EVs still rely on old lead-acid batteries? This article will examine the role of the 12V battery in electric cars, why lead-acid technology is still used, alternatives being explored, and what the future may hold for EV battery technology.

How Electric Cars Work

Electric cars use large high-voltage battery packs to power the drivetrain motor(s) that propel the vehicle. The big battery pack is what gives EVs their all-electric driving range. This high voltage system is completely separate from the standard 12-volt system that powers items like lights, computers, radios, power windows, etc. So while the high voltage battery pack replaces the engine and fuel tank, EVs still need a standard 12-volt battery like gas-powered cars.

The high-voltage battery pack ranges from 24 kWh for shorter range EVs to 100 kWh for premium long range vehicles. This battery pack uses lithium-ion cell chemistry which offers high energy density and efficiency. The cells are assembled into large modules which are then assembled into a full high-voltage battery pack. Sophisticated battery management systems monitor individual cells and control thermal regulation.

In contrast, the 12V lead-acid battery used in EVs is much smaller, typically around 50Ah. This battery is used to power the vehicle's auxiliary electrical system. It supplies power to items like interior and exterior lights, infotainment system, power windows and seats, sensors, on-board computers, safety systems, DC-DC converter and more. While the high-voltage battery pack directly powers drive motors, the 12V battery provides power when the car is turned on before driving.

The Role of the 12V Battery

The 12V battery plays several important roles in an electric vehicle:

• Powers the control systems - The 12V battery powers the vehicle's main computers, control modules, sensors and onboard electronics that control drivetrain, battery management, braking, driver aids and more. These systems need to be live even when the high-voltage system is off.

• Allows pre-drive power - The 12V battery powers accessory systems like lights, radio, power windows before the high-voltage system and drive motors are activated. This allows pre-drive functionality.

• Powers safety systems - Safety features like airbags, emergency braking and door locks rely on the 12V battery as a backup power source in the event of HV system failure or a collision.

• Powers DC-DC converter - The DC-DC converter steps down high voltage from the battery pack to charge the 12V battery when driving. The 12V battery is in turn used to power accessory systems while driving.

• Facilitates vehicle communications - Low-voltage control modules and computers communicate via CAN bus networked systems powered by the 12V battery.

• Backs up HV battery regeneration - Under hard braking, the HV battery can't always accept full regen current. The 12V battery helps absorb and buffer regen energy in these situations.

So in summary, the 12V battery facilitates power, control and communications before driving, during driving, and in emergency situations. EVs still need a 12V battery system similar to conventional cars.

Why Lead-Acid is Still Used

Given the high-tech nature of EVs, it may seem surprising that the simple, old lead-acid chemistry still predominates for the 12V battery. There are some good reasons lead-acid technology remains standard in EVs:

• Proven reliable technology - Lead-acid batteries are a mature technology with well-understood characteristics. Their reliability has been proven over decades of use.

• Low cost - Lead-acid batteries are inexpensive compared to alternatives. Large production volumes keep costs down. Lithium-ion is still much more expensive.

• Availability - Many manufacturers produce lead-acid batteries, so supply is ample. Other chemistries have fewer suppliers.

• Safety - Spilled lead-acid is less flammable than lithium-ion. This is especially important since the 12V battery is usually in the cabin.

• Operating temperature range - Lead-acid tolerates hot and cold temperatures well. Some alternates like NiMH have poorer cold weather performance.

• Recycling - Almost all lead-acid batteries are recycled, keeping toxic materials out of landfills. Recycling is well-established.

• No strict weight limits - Weight is less critical for the smaller 12V battery so very light alternatives are not essential.

• Current capabilities - Lead-acid has high surge current ability for powering vehicle accessories and safety systems.

So in summary, lead-acid technology provides a good combination of proven reliability, low cost, availability, safety, temperature resilience, recyclability and current capabilities. Moving to another chemistry would introduce risks and higher costs.

Alternatives to Lead-Acid

While lead-acid remains dominant for 12V EV batteries currently, alternatives are being explored and developed:

Lithium-Ion - Li-ion is emerging as a potential replacement offering lighter weight and better cold-cranking ability. Cost remains far higher than lead-acid however. Safety concerns due to flammability may limit usage to low-capacity 12V batteries.

Nickel-Zinc - Ni-Zn offers a 40% weight savings over lead-acid. It has longer cycle life but poorer cold cranking performance. Cost is also higher. Safety risks are being evaluated.

Nickel-Iron - Ni-Fe provides comparable life to lead-acid with lower environmental impact. However, its very low energy density results in larger, heavier batteries. Cost is several times higher.

Sodium-Ion - Na-ion has potential for low cost due to sodium's natural abundance. Performance is still inferior to Li-ion however. Chemistry is still under development.

Solid State Batteries - Solid electrolytes could enable Li-ion batteries with high power, long life and improved safety. High costs remain a barrier to commercialization presently.

Ultracapacitors - Supercapacitors offer exceptional power density and cold weather performance. Disadvantages are higher self-discharge and high cost. They may supplement or hybridize with battery chemistries.

So in summary, lithium-ion is the most viable short-term alternative but cost remains a big barrier for now. Other chemistries offer unique advantages but also have performance or economic shortcomings compared to proven, inexpensive lead-acid technology.

The Future of 12V Batteries

The future of 12V batteries in EVs will likely see incremental improvements but no major revolutions in the near-term:

• More premium EVs may adopt lithium-ion 12V batteries as costs gradually decrease. This will provide weight savings and better cold weather performance.

• Mild hybrid lead-acid designs will emerge, reducing size and weight while improving fuel economy.

• Lead-acid formulations will continue improving energy density, cycle life and cold cranking ability.

• Battery monitoring and management systems will become more sophisticated, improving state of charge accuracy and life span.

• Solid state lithium-ion will see gradual introduction later in the 2020s as costs reach mass-market viability.

• Lower voltage systems may be explored, such as a shift to 48V systems which allow downsizing lead-acid batteries.

• Greater integration and right-sizing of power systems will optimize the high voltage and 12V systems.

In summary, the 12V battery is likely to see continued incremental improvements in performance, integration and intelligence, but lead-acid technology will remain dominant through at least 2030. Revolutionary changes may emerge in the 2030s if technologies like solid-state batteries fulfill their promise and reach cost-competitiveness.

Conclusion

In conclusion, electric vehicles still rely on conventional 12V lead-acid batteries due to this technology's proven reliability, low cost, abundance and performance capabilities. The 12V battery fulfills essential roles powering electronics, safety systems and vehicle controls. Alternatives like lithium-ion are emerging but remain far more expensive. Lead-acid battery performance will continue improving incrementally but remain the dominant choice in EVs for years to come until disruptive technologies like solid-state batteries prove themselves and come down in cost. So while electric car technology is transforming, the 12V battery remains old school.