Is Capacity the Higher, the Better?
In today’s society, most people use lithium batteries as a power source due to their small size, light weight, and large capacity, which are highly favored by consumers. But have you ever really studied whether the lithium batteries you use regularly are qualified? Is it true that the larger the storage capacity of high-capacity polymer lithium batteries, the better?
For batteries of different models and specifications, especially those with different volumes, the higher the storage capacity, the longer the usage time. Let’s put aside the factors of volume and weight. For high-capacity backup lithium batteries, the higher the storage capacity, the better.
For the same high-capacity backup lithium battery model, the nominal capacity (such as 600mAh) is completely the same, but the specific initial storage capacity measured may be different. For example, one may be 660mAh, and the other may be 605mAh. Does this mean that the 660mAh one is definitely better than the 605mAh one?
In fact, many battery merchants on the market today falsely label the storage capacity in order to achieve financial gain, selling 40A batteries as 80A. It is recommended that you buy batteries from lithium battery manufacturers. The actual situation may be that batteries with higher storage capacity actually have some substances added to the electrode material to increase the initial capacity, which reduces the stability of the electrode, resulting in the battery with higher storage capacity quickly declining after repeated use dozens of times, while the battery with lower storage capacity remains strong.
How to Estimate Battery Capacity Quickly?
If you are worried about overrated polymer lithium batteries, let’s take a look at the calculation method for polymer lithium-ion batteries:
For a quick estimation of the capacity of polymer batteries, a commonly used formula is: storage capacity = thickness * width * length * K (K is measured in mah/mm^3). Within the range of K values (0.07~0.11), the value of K depends on the storage capacity. The larger the storage capacity, the larger the K value, and the smaller the storage capacity, the smaller the K value (which can be understood as the larger the volume, the larger the K value). In fact, K value can be set to 0.1.
For example, for 103450 (10mm thick, 34mm wide, 50mm long), the calculated capacity is 103450*0.1=1700, and the actual capacity is about 1800mAh.
For example, for 603048 (6mm thick, 30mm wide, 48mm long), the calculated storage capacity is 63048*0.1=864, and the actual capacity can reach 900mAh.
Does a larger battery capacity mean longer battery life?
Generally speaking, the two direct factors that affect the range of electric vehicles are the battery and motor size. Therefore, as long as we know these two factors, we can estimate the range of electric vehicles. It is not necessarily true that the larger the battery, the longer the range. The larger the battery, the higher the power of the motor, and the faster the energy consumption. Moreover, the increase in weight of the electric vehicle will decrease the range.
The general specifications of electric vehicle batteries are 48V, 60V, and 72V. These parameters represent the battery voltage. Knowing the voltage alone is not enough to determine the battery capacity. Careful owners will notice that the battery usually indicates 48V12Ah or 48V20Ah. The ampere-hour (Ah) indicates the electric current of the electric vehicle. When the voltage is constant, the greater the current, the stronger the power, and the higher the battery capacity.
The specific calculation method for battery capacity is:
Battery stored energy = rated voltage X rated current
48V20Ah battery specification has a battery capacity of 960W
60V20Ah battery specification has a battery capacity of 1200W
72V32Ah battery specification has a battery capacity of 2304W
Battery capacity represents how many watts of electric power the electric vehicle can store. This also determines the upper limit of the driving distance. In addition, the power of the motor also needs to be considered, which determines the power and speed of the electric vehicle.
Currently, manufacturers on the market equip 48V batteries with 350W-400W motors, with the highest speed around 25KM. 60V batteries are equipped with 800W motors, with the highest speed around 40KM. 72V manufacturers equip 1000W motors, with the highest speed around 45KM.
Knowing the battery capacity and motor power, we can calculate how long an electric vehicle can run at the most ideal speed:
Electric vehicle driving time = (battery capacity in watts/motor power) total mileage = time * speed
If it is a 48V20Ah battery with a 400W motor, it can run for 2.74 hours, and the range is 60 kilometers.
If it is a 60V20Ah battery with an 800W motor, it can run for 1.5 hours, and the range is 60 kilometers.
If it is a 72V32Ah battery with a 1000W motor, it can run for 2.3 hours, and the range is 103.5 kilometers.
The above is the range in ideal conditions. The actual range depends on the efficiency of converting electrical energy to kinetic energy. A good motor brand will have less loss in converting electrical energy to kinetic energy, which means higher efficiency.
Comparing 60V32Ah battery with 72V20Ah battery, and 48V32Ah with 60V20Ah battery, when the vehicle is equipped with a 60V32Ah battery, the motor is at 600W-1000W, and the normal cruising range can reach more than 100 kilometers. However, if the motor remains the same and the 72V20Ah battery is selected, the normal cruising range is only 70-80 kilometers. When the vehicle is equipped with a 48V32Ah battery, the motor is at 350-400W, and the normal cruising range is generally around 100 kilometers. However, if the motor remains the same and is matched with a 60V20Ah battery, the normal cruising range is around 60-80 kilometers. Through comparison, we can find that generally, the larger the Ah, the farther the cruising range, and the more advantages it has.
Marginal Effect of Battery
Batteries have a “marginal effect”, and blindly increasing capacity is not advisable. To understand the “marginal effect”, we must first know what “marginal” means. From an economic perspective, it refers to the utility brought by each additional unit of goods. In simpler terms, the margin is the “incremental” brought by the “incremental”. The marginal effect is the additional enjoyment that you can get from consuming one more unit of goods.
For example, when you are very hungry, the first hamburger satisfies you a lot, and it brings you a high utility. However, the second hamburger is not as satisfying as the first one, the marginal effect is less, and by the third or fourth, this satisfaction gradually decreases, which is called “diminishing marginal effect”.
Therefore, the “marginal effect” applied to batteries in new energy vehicles, according to the law of marginal balance, is not that the more batteries, the longer the cruising range. The most important thing is that if pure electric vehicles blindly pursue the stacking of large-capacity batteries, it will also cause a steep increase in battery costs. At the same time, the difficulty of battery layout will also increase, which will make car companies have to spend extra research and development costs on battery structure layout. As a result, the production cost of pure electric vehicles will increase, and these costs will have to be borne by consumers when they enter the market, which will increase consumer pressure to buy cars.