Flat top vs Button top
Flat top and button top cells are terms used to describe the shape of the positive end of a cylindrical battery cell, such as an 18650 battery.
A flat top cell has a flat positive terminal on the top of the battery, while a button top cell has a small protruding button-shaped positive terminal.
The choice between flat top and button top batteries is important when selecting batteries for certain applications. Devices that require a tight fit, such as flashlights or certain electronic devices, may require flat top batteries. Devices that require a slightly longer battery with a protruding positive terminal, such as certain types of flashlights and CCTV door bells, may require button top batteries.
These extra few millimetres can be the difference between a battery that fits and a battery that doesn't. If in doubt, look at the existing batteries that came with your device, consult a manual, or contact the manufacturer. For spring-loaded batteries, like flashlights, it shouldn't make a huge difference.
It's important to note that the physical differences between flat top and button top batteries may affect how they fit and function in different devices. Always check the manufacturer's specifications to ensure that you are using the correct type of battery for your device.