When buying 18650 batteries, you will have the option between button top and flat top batteries.
Protected batteries, as the name might suggest, have a small electronic circuit built into the battery packaging. This is on one end of the battery and is indistinguishable from other batteries.
This circuit protects the battery against hazards such as overcharging and discharging, short circuits and extreme temperatures. This is designed to protect the devices you use them on and to avoid damage by explosion or leakage.
Many protected batteries also have a valve that permanently disables the battery if the pressure is too high inside the battery.
This is usually what happens when the batteries swell, at a time when they are more susceptible to catching fire.
An unprotected battery lacks this circuit. They are therefore cheaper and are also susceptible to problems that such safeguards are designed to avoid.
If you select an unprotected cell (and many of the best cells are not protected), you should take extra care when selecting and using your battery.
Pay particular attention to the discharge rating (CDR) to make sure you don’t drain excess power from a battery, or it might overheat.
You also need to keep your contacts private, ideally in a plastic case so that the battery won’t go missing in your pocket or bag. You also need to make sure you don’t leave the battery in the charger for too long.
When in doubt, buy a better quality battery even though it is a bit more expensive.
The button top vs flat top 18650 batteries
To really demonstrate how standardized the 3.7v 18650 rechargeable battery is, there are two small variations in size: flat top and button top. The button top batteries are popular for the tactical flashlight under $30
This has to do with contacts, especially positive contacts. The button’s top battery will protrude slightly, while the flat top battery is completely flat.
These extra millimeters could be the difference between a suitable battery and a non-battery. If in doubt, check the batteries available with your device, refer to the instruction manual or contact the manufacturer.
For spring-loaded batteries, like flashlights, it doesn’t make a big difference.
How to avoid buying fake 18650 batteries
Like any branded product, be careful with fake 18650 batteries. It is very common for many suppliers to buy cheap batteries, rewrite them as trademarks, and market them as genuine items.
This is not only wasting your money but also potentially dangerous. If you buy a battery for a high-capacity device, believing it has a full safety CDR, you could injure yourself or damage your device when the battery has a completely different rating.
The battery scammers are good at what they do. A genuine and fake battery is difficult to distinguish. From bundles to branding, to online listings, they look like real deals. The only way you can say fake from genuine batteries is by weight.
Most brands have made the weight of their original batteries available somewhere. You should cross-reference any batteries you buy online with the manufacturer’s specifications. Even spelling mistakes do not indicate spoofing, as a genuine manufacturer had to point out through a Facebook update.
To test a particular cell, try an internet search for its name, followed by a Google data sheet. This will list the battery weight, capacity and maximum CDR.