Complete Guide to Lithium-Ion Battery Sizes: A Practical Guide from Model Identification to Selection

Part 1: What Is a Lithium-Ion Battery?

A lithium-ion battery is a rechargeable battery, like a "lithium-ion transporter," that stores and releases energy through the migration of lithium ions between the positive and negative electrodes. Its core components include:

• Cathode (Positive Electrode): Commonly uses lithium cobalt oxide (high energy, suitable for phones) or lithium iron phosphate (high safety, suitable for electric vehicles); it's the "departure station" for lithium ions.

• Anode (Negative Electrode): Usually made of graphite, which acts like a layered "parking lot" that can embed lithium ions.

• Electrolyte: Responsible for transporting lithium ions while preventing direct contact between the electrodes that could cause a short circuit.

  
  

Three Major Advantages of Lithium-Ion Batteries (Most Relevant to Users):

1. Longer Battery Life: 2–3 times higher energy density than traditional NiMH batteries. Devices like phones can last longer with batteries of the same size.

2. Low Self-Discharge: After being fully charged and left for 3 months, it loses only about 5% of its charge (NiMH batteries can lose up to 30%).

3. Longer Lifespan: Can handle over 500 charge-discharge cycles under normal conditions. If charged once a day, it can last 2–3 years. Actual lifespan is significantly affected by factors such as depth of discharge and temperature. For example, frequently discharging the battery close to empty before recharging will consume more cycles than using it within a moderate range (e.g., 20%–80%).

Part 2: Common Lithium-Ion Battery Sizes and Application Scenarios

Cylindrical Batteries: The "main force" in industrial and consumer electronics

Using the 18650 battery as an example, its naming convention indicates that "18" stands for a diameter of 18mm and "65" represents a height of 65mm. This standardized naming makes it easy to quickly identify battery sizes. In practical applications, multiple 18650 batteries are often connected in series or parallel in laptops to meet different voltage and capacity requirements.

The 4680 battery was first introduced by Tesla in 2020, featuring a diameter of 46mm and a height of 80mm. Compared to traditional 1865 and 2170 batteries, it offers significant advantages in energy density, production cost, and charging efficiency. The energy of a single cell is increased by five times, the overall vehicle range can be extended by 16%, and compared to tabbed batteries, the power is increased by six times, with a sixfold improvement in power output. In 2025, Tesla began mass production of the 4680 battery at its Gigafactories in Texas (USA), Berlin (Germany), and Shanghai (China), applying it to models such as the Model Y and Cybertruck.

Other Battery Shapes: Catering to Special Application Needs
Prismatic (Rectangular) Batteries:
Common sizes include 103450 (10×34×50mm), typically used in smartphones and tablets. These batteries can be customized to fit the device’s shape, maximizing space utilization up to 90%.

Pouch Batteries (Polymer Batteries):
These have no fixed size and can be as thin as 0.5mm, making them especially suitable for weight-sensitive applications like drones. Taking the YLP polymer battery as an example:

• Weight Advantage: Using aluminum-plastic pouch packaging and gel electrolyte, it is 20%-30% lighter than the 21700 battery, reducing drone body load and extending flight time at the same capacity.

• High Energy Density: By optimizing electrode materials, the energy density is 10%-15% higher than that of conventional cylindrical batteries. For instance, the 4S 14.8V/5000mAh model can support drones to fly an additional 10-15 minutes.

• Shape Customization: Can be designed into curved, trapezoidal, or other irregular shapes according to the drone battery compartment, improving space utilization to 90% and avoiding the gap waste seen with cylindrical batteries.

Part 3: Why Does Battery Size Affect Device Performance?

1.Larger Size May Mean Longer Battery Life, But Not Always!

• Example: Tesla Model 3 upgraded from 18650 to 21700 batteries, increasing the battery pack’s energy density from 250Wh/kg to 300Wh/kg, resulting in a 15% range increase (about 90 km more). This is because the 21700 battery is larger (21mm diameter) and can hold more “active material,” assuming the same chemistry (e.g., both use ternary lithium). From a technical perspective, battery capacity closely relates to the active material loading on the electrodes and the specific surface area of electrode sheets. Larger batteries can accommodate more active material in their design, thereby increasing capacity. However, material system differences also greatly affect capacity; for example, batteries of the same size using high-nickel ternary materials can have 10%-20% higher capacity than those with regular ternary materials.

2.Shape Influences Device “Form Factor”

• Cylindrical batteries (like 18650) resemble soda cans and leave gaps when arranged, with about 60% space utilization.

• Pouch batteries are like “small pillows” and can be customized to device shapes (e.g., curved batteries for foldable phones), achieving up to 90% space utilization and allowing devices to be slimmer and lighter.
  From an engineering standpoint, internal device space is limited, and how well the battery shape fits determines usable space. Due to their flexibility, pouch batteries can better conform to irregular device interiors, reducing wasted space and enabling higher-capacity batteries within limited volume, thus enhancing overall device performance.

Part 4: How to Choose the Right Battery Size for Your Device?

A Four-Step Selection Method (Easy for Everyone to Understand):

① Calculate How Much Power the Device Needs

• Example: For a 10W laptop aiming for 5 hours of battery life, the required battery capacity ≈ (10W × 5h) / 3.7V ≈ 13.5Ah = 13,500mAh. You can choose 4 pieces of 18650 batteries (each 3500mAh) connected in parallel to meet the power demand. In real calculations, factors like the battery discharge voltage platform and device power consumption fluctuations should also be considered. Professionals use the device’s power consumption curve combined with the battery’s discharge characteristics curve to precisely calculate the capacity needed to ensure stable power supply throughout operation.

② Measure the Battery Compartment “Room Size”

• Use a ruler to measure the length, width, and thickness of the battery compartment. For example, if a drone’s battery compartment is 50mm × 30mm × 20mm, you cannot pick a battery that’s too large.

• Pay attention to tolerances: cylindrical batteries have diameter tolerance ≤ ±0.1mm; pouch batteries have thickness tolerance ≤ ±0.2mm, otherwise, the battery won’t fit. For high-precision devices like aerospace, tolerances may be tighter, around ±0.05mm. Professional battery manufacturers use high-precision molds and automated production to strictly control size tolerances, ensuring every battery perfectly fits the device.

③ Balance “Weight” and “Battery Life”

• For drones: prioritize YLP pouch batteries (polymer type), which are 20%-30% lighter than 21700 cells and offer 10%-15% higher capacity, extending flight time by 10-15 minutes.

• For power banks: pouch batteries are lighter and more portable; for the same capacity, they weigh about 30% less than cylindrical batteries.
  From the perspective of energy density (Wh/kg) and specific power (W/kg), different scenarios have different requirements. Drones require high specific power batteries for rapid power output, while maintaining enough energy density for flight time. Power banks prioritize energy density to store more power within limited weight. YLP can provide tailored “weight vs. endurance” optimized solutions for different applications.

④ Refer to Industry Practices

• Laptops: primarily 18650, some high-end models use 21700;

• Smartphones/Tablets: pouch batteries (extra thin);

• Electric vehicles: Tesla uses 21700 and 4680 cells in some models;

• Drones: mainstream use pouch batteries (e.g., YLP 4S 14.8V/5000mAh high-rate models);

• Smartwatches: pouch batteries (1-2mm thick, 100-300mAh capacity).

Industry battery selection experience is built on long-term practice and balances cost, performance, safety, and other factors. YLP, as a professional battery manufacturer, keeps pace with industry trends, continuously optimizes product performance, and provides expert selection advice to help customers quickly find the most suitable battery solutions for their devices.

Part 5: Common Questions About Battery Size

1. Does a Larger Battery Always Mean Higher Capacity?
   Not necessarily! Capacity also depends on the materials used. For example, the 26650 battery:

• Using lithium iron phosphate (LiFePO4) material, capacity is about 2400mAh;

• Using ternary lithium materials, capacity can exceed 5000mAh. Even with the same large size, ternary lithium batteries can store more energy. From a materials chemistry perspective, different cathode materials have different crystal structures and lithium-ion intercalation mechanisms, resulting in varying theoretical specific capacities. Lithium iron phosphate has a theoretical capacity of about 170mAh/g, while high-nickel ternary materials can reach 200–220mAh/g, causing significant capacity differences for batteries of the same size but different chemistries.

1. Can Different Sized Batteries Be Mixed?

• Cylindrical batteries like 18650 and 21700 differ in diameter and length and cannot be directly swapped;

• For pouch batteries with similar sizes, first check if voltages match (both usually 3.7V), and they must be managed with a battery management system (BMS) to avoid damage.
  From a circuit perspective, different sized batteries have varying internal resistances, capacities, and charge/discharge characteristics. Mixing them can cause imbalance within the battery pack, leading to overcharge or over-discharge of some cells, severely shortening battery life and causing safety risks. YLP’s BMS uses advanced intelligent algorithms to monitor each cell’s state in real time, effectively balancing the pack and ensuring safe, stable operation—even in complex mixed battery scenarios (under certain conditions).

1. How Will Batteries Evolve in the Future?

• Larger cylindrical batteries: The 4680 battery is already widely used in some Tesla models, and its energy density and production processes will continue to improve. Future batteries might become even larger and higher-performing, further boosting EV range and power.

• Thinner pouch batteries: Thickness could shrink to 0.3mm or less, fitting foldable phones, wearables, and other devices demanding extreme thinness, improving portability and wearing comfort while maintaining battery life.

Industry trends show that with ongoing advances in materials and manufacturing, battery size and performance will keep improving. Large cylindrical batteries enhance energy density by increasing active material loading and optimizing internal structure, while pouch batteries push breakthroughs in thinness and safety.

Part 6: Pro Tips for Professional Battery Selection

• Buying off-the-shelf batteries: Provide your device model (e.g., “Brand X Laptop”) or the old battery’s model number (e.g., “18650-3.7V-2000mAh”);

• Custom batteries: For special shapes (e.g., curved drone batteries), contact YLP with the battery compartment dimensions—samples can be made within 7 days;

• Safety first: Choose batteries with certifications (UN38.3, CE, etc.), avoid uncertified “three-no” products to prevent swelling or fire hazards.

As an industry-leading manufacturer, YLP has a professional R&D team and advanced production equipment with strong customization capabilities. Whether standard sizes or complex shapes, YLP offers fast design, prototyping, and mass production services. All YLP batteries strictly comply with multiple international safety standards, ensuring safety from the source and giving customers peace of mind.

Choosing the right battery size helps your device run longer without becoming bulky. If you have more questions, feel free to contact us for one-on-one selection support!