18650 battery which side is positive and negative

What is an 18650 battery?

An 18650 battery is normally a lithium ion or lifepo4 battery. The height is 650mm. and diameter is 18mm. As we can see from the dimensions. The 18650 battery is named from its size. So, if any cell rated this size, we can call it 18650 cells.   flat top

All battery cells with positive and negative pole.


Same for 18650 battery cells. but we should have different way to find out the positive and negative pole of it. This is very important to know before you insert the battery to the device. Wrong setting would lead a fire or other problem if there is no protection circuit.

Check by sight.

We can find out the positive and negative by just see it. The flat side is negative most of the time. and top bottom side is positive. This a normal design as most of the battery cell like this.

However, this is not 100% for sure. Because sometimes both sides are flat. And some batteries positive and negative just in one side like following photo shows.

Check by meter.

We strongly recommend to check the 18650-cell pole by a volt meter. This will be 100% safety before you place the battery to any devices.