18650 lithium batteries are mostly used in laptop batteries due to their high capacity per unit density. In addition, because of their excellent stability during operation, 18650 batteries are widely used in various electronic fields: they are commonly used in high-end flashlights, portable power supplies, wireless data transmitters, electrically heated clothing and shoes, portable instruments, portable lighting equipment, portable printers, industrial instruments, medical instruments, etc.
So how do you choose a high-quality 18650 lithium-ion battery? Choose the most suitable 18650 lithium battery based on your electrical equipment, considering factors such as brand, voltage, capacity, continuous discharge rate, and battery life. Most importantly, choose a battery with high safety. Below, we will elaborate on these points in detail:
1. Brand
Regarding brands, reliable options include internationally renowned brands like Sanyo, Samsung, Sony, and LG. Sanyo and LG focus on conventional applications, primarily high-powered flashlights, power banks, and laptop batteries. Sony specializes in high-powered, high-current applications. For example, the VTC4 can discharge up to 30A, easily handling applications like e-cigarettes and toys.
2. Nominal capacity
The nominal capacity of an 18650 battery is related to its battery life, and the unit is "mAh". The higher the capacity, the longer the battery life. For example, a 2800mAh battery can discharge continuously for 2 hours at a current of 1.4A.
3. Continuous Discharge Current (CDR)
Continuous discharge capacity is expressed in C-number, and continuous discharge current = continuous discharge capacity C-number × capacity. For example, if an 18650 battery has a capacity of 2800mAh and a continuous discharge capacity of 0.5C, then the continuous discharge current = 1.4A. Discharging at a rate exceeding 1.4A for an extended period will severely affect battery life and may even lead to overheating, combustion, or explosion.
5. Internal resistance
Internal resistance is the battery's own resistance. The lower the internal resistance, the less it consumes and the stronger its discharge capacity. This parameter is usually listed on the battery's product page, so pay attention to it when purchasing. Try not to buy cells with an internal resistance exceeding 100mΩ. When using multiple 18650 batteries in series, be sure to buy batteries of the same brand and model; otherwise, batteries with high internal resistance and low capacity will become a bottleneck.
6. Temperature
Temperature is a major factor affecting the lifespan of 18650 lithium batteries. The higher the temperature, the faster the battery ages and the greater the damage to the battery's internal structure.
7. Pointed head and flat head
18650 lithium batteries come in flat-tip and pointed-tip versions. As shown in the image, the positive terminal on the left has a protruding tip (pointed), while the positive terminal on the right has no protrusion (flat). Generally, I recommend purchasing pointed-tip batteries to ensure compatibility with more devices and applications. Flashlights typically use a spring-loaded design for their positive and negative terminals, allowing them to be used with both pointed and flat-tip batteries. However, when using flat-tip batteries in series, the positive terminal of the flat-tip battery cannot reach the negative terminal of the other battery.
8. With and without protective plate
The pointed-tip 18650 comes with a protection board, while the flat-tip 18650 does not. The 18650 lithium battery with the protection board is a few millimeters taller than the one without, and is also slightly more expensive, but it is safer and more versatile. The 18650 lithium battery with the protection board can prevent the battery from being over-discharged, which can cause the lithium battery to overheat, or even burn or explode.
Of all 18,650 lithium-ion batteries, LiSOCl2 has the highest energy density and the longest lifespan, reaching 15 to 20 years. This type of battery is particularly suitable for devices with low and relatively short power supply currents. It also boasts a long lifespan, low self-discharge rate, and excellent environmental resistance.
