Power battery terminology differs from traditional physics, which uses terms like voltage, current, resistance, and charge. Instead, it uses terms like electrical energy, power, capacity, and charging rate. What’s the relationship between these terms?
Let’s break it down and see if you understand everything.
These two terms represent two different fields. So where is the connection?
In physics, electricity works like this:
2026 Xiaomi SU7 Official Power Battery Data:
SU7 Standard Version: 73 kWh, Lithium Iron Phosphate (LFP), High Voltage Platform: 752 V
SU7 Pro: 96.3 kWh, Lithium Iron Phosphate (LFP), High Voltage Platform: 752 V
SU7 Max: 101.7 kWh, Ternary Lithium (NCM), High Voltage Platform: 897 V
In reality, power batteries are just different units and names; the formulas remain the same. First, let’s look at the corresponding relationships in the table:
First, let’s look at the corresponding relationships in the table:
| Physical Concepts | Power Battery Terminology | Simplified Explanation |
| Energy Charge (Q) | Capacity (C/Ah) | Energy charge is the number of electrons (coulombs), Q=It, which is also the mathematical root of all “capacity and rate” in power batteries. Power batteries: directly say “how much electricity can be stored”. The unit is **Ah (ampere-hour)**, for example, 10Ah means that 1A of current can discharge for 10 hours. For users, capacity (Ah) is much more intuitive than the abstract “coulomb”. |
| Voltage (U) | Voltage / Plateau | Voltage is the potential difference. Power batteries: Voltage determines how powerful the equipment can be driven. However, batteries are more concerned with the **”voltage plateau”** (whether the voltage is stable during discharge), because a rapid voltage drop means the battery is almost depleted. |
| Current (I) | Rate (C-rate) | Current is the flow rate. Power batteries: don’t say “5A current”, but “1C discharge”. C = Capacity. A 10Ah battery has a 1C rating of 10A. This is a relative value; regardless of battery size, 1C represents the “full load” state, facilitating comparisons of different battery performance. |
| Power (P=U*I) | Power / Rate | How fast work is done. Power battery: Directly determines acceleration performance. High rate (e.g., 3C, 5C) = High power = Strong acceleration. |
| Electrical Energy (W=UIt) | Energy (Wh/kWh) | The total amount of work done by current. Power battery: kWh (kilowatt-hour), directly tells you how far you can travel. W=UQ; once you know the voltage and capacitance of the power battery, you can naturally calculate the electrical energy. |
This “language difference” is essentially a difference between the perspectives of physics (fundamental theory) and engineering (application and practice).
Simply put: physics teaches you “why,” while power battery terminology teaches you “how to use it.”
Similar to a course on “Automotive Theory,” both are essentially about dynamics, but it doesn’t focus on pure mechanics; it focuses on vehicle performance. Is the new SU7’s performance impressive?
The Difference in Core Perspectives: Microscopic vs. Macroscopic
– Physics (Microscopic/Ideal): Focuses on circuit principles. It views the battery as an ideal “power source,” studying how electrons move in the wires (current), how much thrust they exert (voltage), and how much resistance they encounter (resistance). This is to establish a basic physical model, usually ignoring the battery’s own wear and tear and aging.
– Power Battery (Macroscopic/Practical): Focuses on the energy carrier. It views the battery as an “energy warehouse.” Engineers are concerned with: how much energy this warehouse can hold (capacity), how fast it can unload (rate of return), and its total value (electrical energy).
Why does the power battery industry need its own set of terms?
In short, it’s a convenient “shortcut” for engineers’ design and car owners’ use. Specifically:
(1) To quantify “range”: The unit of “energy (Q)” in middle school is too small (coulombs), making it difficult to calculate range. Power batteries use Ah (capacity) and kWh (energy), so car owners can immediately tell whether it can travel 500 kilometers or 600 kilometers.
(2) To describe “performance”: The unit of “current (I)” in middle school is an absolute value. Power batteries use rate (C), a relative value. Whether it’s a mobile phone battery or a truck battery, 2C represents “strong instantaneous burst capability,” facilitating horizontal comparison.
1C takes 1 hour to fully charge. 2C takes 0.5 hours. 0.5C takes 2 hours. The value before C multiplied by the value before the hour equals 1.
(3) To assess “lifespan”: Middle school doesn’t consider what happens when the battery fails. When discussing power batteries, we need to consider cycle life (number of charge-discharge cycles), internal resistance (heat loss), and SOC (state of charge/remaining capacity). These are all practical issues that must be addressed in engineering applications.
Practice Exercise
The official battery data for the 2026 Xiaomi SU7 is as follows:
SU7 Standard Edition: 73 kWh, Lithium Iron Phosphate (LFP), High Voltage Platform: 752 V
SU7 Pro: 96.3 kWh, Lithium Iron Phosphate (LFP), High Voltage Platform: 752 V
SU7 Max: 101.7 kWh, Ternary Lithium (NCM), High Voltage Platform: 897 V
Based on the above information, how do you determine if the data in the table below is correct? How do you verify it?
