What's the difference between a protected battery and an unprotected battery?

[rainbowbright]

I recently found some online ads for some protected 18650 batteries and some unprotected 18650 batteries. What's the difference? I've also seen some flashlight ads that specifically state that the flashlight may not be compatible with an unprotected battery. Does this mean that the protected batteries are thicker or something?

 

[TigerhawkT3]

Some cells are a bit larger than others, but that's more to do with loose manufacturing tolerances.

Also, from the Welcome Mat:

Q: What do protected/unprotected mean in regards to Lithium-Ion?
A: As mentioned in the "what is double-tapping" question, a "protected" Li-Ion has a small electronic circuit integrated into the cell packaging. It protects against common dangers, such as overcharge, overdischarge, short-circuit (overcurrent), and temperature. These cells are safer to use, both individually and in batteries. They are less likely to ignite and cause personal or property damage, a phenomenon known as "venting with flame." Unprotected cells do not have this protection circuit, so they can have more capacity and current capability than protected cells. Some cells, such as 10440 (AAA), are too small to accomodate a protection circuit and are only available in unprotected form. Users must decide whether they prefer to stick with protected cells or accept the bigger responsibility and danger associated with unprotected cells.

 

[LuxLuthor]

I recently found some online ads for some protected 18650 batteries and some unprotected 18650 batteries. What's the difference? I've also seen some flashlight ads that specifically state that the flashlight may not be compatible with an unprotected battery. Does this mean that the protected batteries are thicker or something?

They are about 2-3mm longer. Here are some pictures I took of protected batteries that show the protection circuit.

 

[Juan334]

just did a google search and this came up it helped alot even though its super old thanks

 

[jasonck08]

just did a google search and this came up it helped alot even though its super old thanks

This link should be helpful as well.