So now we know the energy of a 3.7V 2600mAh battery is 9.62Wh. While mAh only suggests 'two dimensions' of capacity, Wh is a solid 'three dimensions' figure that calculates battery capacity as a whole.ĭon't feel stressed about another unknown terminology.Īh is just a different unit that is equal to 1000mAhįor a 3.7V 2600mAh battery, the Wh will be: It's like telling you how high(3.7V) and how wide(2600mAh) this product is. If you take a closer look, you will find that battery capacity was actually given in 3.7V 2600mAh. When indicating battery capacity, the relationship between mAh and Wh is very similar to the radius and volume of a bucket. They think you don't necessarily need to know the volume.

The product page only tells you the radius and height. Imagine you are looking to buy a bucket online. Relax, the water bucket analogy will help you sort things out over and over again. Didn't you just say Wh stands for battery capacity? How come all the battery capacity was marked in mAh?' If you are buying a replacement battery, you might see their capacity listed in mAh (milliamps hours). Why battery capacity is given in mAh instead of Wh It describes the energy capcity or capacity do useful work stored in the battery. What really matters is the total energy stored in the battery or, in other words, how much water is in the bucket. The other one is smaller in diameter.īut you can't say the first bucket holds more water depending on the size of the bottom area. This calculation seems straightforward, but it's not correct. You have a 3.7V 2600mAh battery, and you are expecting it can power a 600mAh fan for 4 hours or more. This allows it to work, and the little waterwheel will spin as you wish. We move the same quantity (or volume) of water to a slimmer and taller bucket. The jet of water doesn't reach a high enough height to push the waterwheel. It has a bucket sitting next to it with a tap halfway down. In the figure below, you can see this waterwheel contraption. Let's suppose you want to spin a small waterwheel because you enjoy watching the rotation. Here comes the water bucket analogy again. However, the 3.7 voltage is not sufficient to power those devices that require 5V or more. You use it to power a 5V, 3W clip on fan. This value varies among other types of batteries. Nominal voltage depends on the chemistry of the battery.īattery chemistry and their nominal voltage Chemistryįor lithium-ion batteries, the mid-way point is between 3.6V to 3.7V. This sentence sounds complicated to understand. The nominal voltage is a function of anode and cathode materials, as well as impedance. Why isn't it 1.1V, 2.3V, or any other arbitrary number? You may wonder, why the nominal voltage of a 18650 battery has to be 3.6V or 3.7V. Nominal voltage is often the midpoint of that range.Ĭell manufacturers mark the nominal voltage of their lithium-ion as 3.6V or 3.7V.įor marketing purposes, some manufactures would mark it as 3.7V on the package to imply that it's more powerful. It then drops rapidly to around 3.2V, until it stops working altogether.įrom the graph, you can see that most of the time, it remains at around 3.7V midway through the discharging cycle. It begins at 4.2V and decreases slightly. The voltage of 18650 lithium battery doesn't decrease evenly. So you know that voltage decreases when the battery is running/discharging, and increases again when the battery is being charged. When the water is consumed, the water level declines. Water level, indicating the height of the water, is somehow very similar to voltage.īecause they are both used to gauge the range, difference between the lowest and highest. We can think of the 18650 battery as a bucket of water. Voltage, or electrical pressure, is the difference in electric potential between two points. The next two numbers (65) stand for the height, and the final number (0) means the shape of the battery. The first two numbers(18) refer to the diameter of the battery in millimeters. Just like other lithium-ion cells, the 18650 battery is named after dimensions.