18650 lithium batteries do not universally include protection circuits (PCBs), and their presence depends on the intended use and manufacturer design.

Bare 18650 cells, often sold for industrial or DIY applications, lack protection circuits. These “unprotected” cells are cheaper and smaller, appealing for space-constrained projects where the device itself incorporates external protection (e.g., laptop battery packs with built-in BMS). However, they pose risks: overcharging can cause overheating or explosion, while over-discharging below 2.5V permanently damages capacity. Short circuits may also lead to thermal runaway, as there is no mechanism to cut off current flow.

In contrast, “protected” 18650 cells integrate a small PCB (typically at the negative end) with protection features: overcharge protection (cuts off charging at ~4.2V), over-discharge protection (shuts down below ~2.5V), overcurrent protection (limits excessive current during short circuits or high loads), and sometimes temperature protection (activates at extreme heat). These are common in consumer products like flashlights, power banks, or vaping devices, where user safety is paramount.

The decision to include a protection circuit depends on the application. Manufacturers omit it when the host device has robust external protection, reducing cost and size. For example, electric vehicle battery packs use unprotected 18650 cells but rely on a centralized BMS to manage charging, discharging, and safety. Conversely, standalone cells sold to general consumers often include protection to prevent misuse.

It is crucial for buyers to check specifications: protected cells are labeled as such, while unprotected ones may be described as “bare” or “industrial grade.” Using unprotected cells without external protection is risky and requires strict adherence to voltage and current limits.

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