Which battery should be chosen for electric vehicles, lead-acid or lithium batteries?

Today, with the rapid development of electric vehicle technology, batteries, as the core power source, their performance and safety directly determine the vehicle's user experience and user trust. At present, lead-acid batteries and lithium batteries, which dominate the market, are like two "power hearts" with different personalities, each demonstrating its advantages in specific scenarios. This article will conduct an in-depth analysis from dimensions such as performance, security, and cost to help you find the most suitable choice.

I. In-depth Comparison of Performance Parameters
1. Energy density and battery life
Lithium batteries: Their energy density is an absolute advantage. Mainstream products can reach 150-260Wh/kg, and some high-end products even exceed 300Wh/kg. This means that under the same weight, the storage capacity of lithium batteries is 3 to 5 times that of lead-acid batteries. In actual performance, taking a 48V battery pack as an example, a 5kg lithium battery and a 15kg lead-acid battery have similar volumes, but their ranges can differ by 50% to 80% (such as 80km vs 50km).
Lead-acid batteries: Their energy density is only 30-50Wh/kg. Due to material properties, their weight is usually 3-4 times that of lithium batteries of the same capacity. This not only increases the vehicle's load but also limits the upper limit of the range, which is generally applicable to short trips within 50 kilometers.

2. Charging and discharging efficiency and speed
Lithium batteries: The charging efficiency is between 90% and 95%, and it usually takes only 2 to 4 hours to fully charge. Some products also support fast charging. When discharging, it can be deeply discharged to the remaining 20%, making more full use of the electricity.
Lead-acid batteries: Their charging efficiency is relatively low, approximately 70% to 85%. It takes 8 to 12 hours to fully charge them, and they are not suitable for fast charging; otherwise, it is easy for the plates to fall off, significantly shortening their lifespan. When discharging, it is recommended to retain more than 30% of the battery capacity. Excessive discharge will affect the battery performance.

3. Cycle life and long-term cost
Lithium batteries: The standard cycle life is 1,000 to 2,000 times. If charged three times a week, they can be used for 6 to 12 years. Although the unit price is high, the annual cost averaged out is approximately 60% of that of lead-acid batteries, making it more cost-effective for long-term use.
Lead-acid batteries: They have a cycle life of 300 to 500 times and need to be replaced after 2 to 3 years of normal use. Moreover, when replacing, the recycling value of the old battery is only 10% to 15% of its original selling price. In the long run, the replacement cost is even higher.

4. Environmental adaptability and characteristic performance
Self-discharge rate: The self-discharge rate of lithium batteries is low, ranging from 5% to 10% per month. Even if they are idle for a long time, they can still be started without charging for three months. Lead-acid batteries have a relatively high self-discharge rate of 10% to 20% per month. If they are left unused for a long time for one month, they may be discharged and become unusable.
Low-temperature performance: The capacity retention rate of ternary lithium batteries is approximately 70% at -20 ℃, while that of lead-acid batteries is only around 50%. The low-temperature performance of lithium iron phosphate batteries is slightly weaker, but they remain stable above -10 ℃.
Discharge power: Lithium batteries support high-rate discharge of 3-5 ° C, resulting in minimal power attenuation in scenarios such as electric vehicle acceleration. High-rate discharge of lead-acid batteries is prone to heat generation, and continuous large current output can cause a sudden drop in capacity.

Ii. Comprehensive Assessment of Safety Performance
1. Thermal runaway risk
Lead-acid batteries: They have good thermal stability, with sulfuric acid water solution as the electrolyte. They are non-flammable and non-explosive, and perform stably below 80℃. At most, they may bulge and leak during short circuits. However, long-term overcharging may cause the electrolyte to evaporate, leading to shell rupture and leakage, which is highly corrosive.
Lithium batteries: The thermal stability of different types of lithium batteries varies. Ternary lithium batteries may trigger thermal runaway at around 130℃, releasing toxic gases such as carbon monoxide and posing a risk of explosion and combustion. The thermal runaway temperature of lithium iron phosphate batteries can reach over 200℃, and their safety is significantly better than that of ternary lithium batteries, but their low-temperature performance is slightly inferior. Fortunately, mainstream lithium battery products are all equipped with BMS (Battery Management System), which can monitor temperature and voltage in real time. When the temperature exceeds the limit, it will automatically cut off the power to ensure the safety of use.

2. Security of usage scenarios
Charging safety: Lithium batteries should be charged with the original factory charger. Avoid charging in high-temperature or direct sunlight environments. The charging time should not exceed 8 hours. Lead-acid batteries have a relatively low risk of overcharging, but when charging at night for a long time, they still need to be kept away from flammable materials. Aged batteries may show a "bulging" phenomenon.
Physical protection: Lead-acid batteries feature a steel casing, which is highly resistant to impact and less likely to be damaged by minor collisions. However, their heavy weight leads to a decrease in vehicle flexibility. Lithium batteries mostly adopt aluminum alloy casings and explosion-proof designs. They are lightweight but have relatively weak shock resistance. Severe impacts may cause internal short circuits.

Iii. Comprehensive Selection Guide
Scenarios suitable for choosing lead-acid batteries
Budget-sensitive users: The initial cost of purchasing a car is low, and the battery cost is approximately one-third of that of lithium batteries.
Short-distance fixed routes: such as grocery shopping, picking up and dropping off children, etc., with a daily driving distance not exceeding 30 kilometers.
Limited charging conditions: It can only be charged outdoors or in an environment without temperature control. Lead-acid batteries have stronger resistance to environmental interference.
Low maintenance requirements: No need to understand complex charging rules, making daily use more "worry-free".

Scenarios suitable for choosing lithium batteries
Long-range demand: Daily commuting distance of more than 50 kilometers, or frequent cross-district travel.
Portable charging requirements: The battery needs to be taken home for charging. The weight of a lithium battery is only 5-10kg, while that of a lead-acid battery is 15-25kg, making it more laborious to move.
Performance pursuers: They focus on acceleration power, climbing ability, or frequently carry people and goods.
Long-term usage plan: We hope that the electric vehicle can be used for more than five years and reduce the frequency of battery replacement.

Suggestions for detailed selection of lithium batteries
Ternary lithium batteries: Suitable for users in the north as they have better low-temperature performance. However, it is necessary to choose products with BMS and that have passed the needle-puncture test for better safety.
Lithium iron phosphate battery: Suitable for users in the south or those with extremely high safety requirements, it can have a cycle life of over 2,000 times, providing a longer service life.

Iv. Key Tips for Maintenance and Care
Charging specification
Lead-acid batteries: Perform a deep discharge once a month (fully charge when the battery is completely drained) to prevent long-term undercharging from affecting their lifespan.
Lithium batteries: Keep the battery capacity between 20% and 80% for cycling. For long-term storage, retain 50% of the battery capacity to minimize damage to the battery.

Environmental control
Avoid using or charging in an environment below -20 ℃ or above 60℃. Extreme temperatures can significantly reduce battery performance and lifespan.
On rainy days, prevent water from entering the battery. If a lead-acid battery leaks, neutralize the electrolyte with baking soda in time to avoid corroding the vehicle components.

Tips for extending your lifespan
Lead-acid batteries: Regularly check the electrolyte level. When the electrolyte is low, add distilled water (do not use tap water) to maintain normal battery reaction.
Lithium batteries: Avoid frequent fast charging. Calibrate the battery management system with slow charging once a month to help maintain stable battery performance.

Conclusion
The showdown between lead-acid batteries and lithium batteries is essentially a choice between "stability and practicality" and "high efficiency and advancement". With the maturation of lithium battery technology (such as the research and development of solid-state batteries), its safety is rapidly improving, while lead-acid batteries will still exist in the low-end market for a long time due to their cost advantage. The final decision should be based on core factors such as one's own usage frequency, travel distance, and budget planning - what suits oneself is the best solution.