What do the MAH and WH in the lithium battery label mean?

Most mobile devices and cameras now use lithium-ion batteries, and most consumers do not understand the capacity labels on these batteries, such as what mAh and Wh stand for. Learning to read these signs is simple and practical. One time a friend of mine looked at the camera battery on my desktop and said, "Look how much bigger your camera battery is than my portable battery. Why is it only a little bigger?" This mobile power pack is 5200mAh, compared to the 6600mAh battery for the larger camera. In terms of volume, the camera lithium battery is at least twice as large as the mobile power supply, but 6600 is definitely not twice as large as 5200 in terms of numbers. Is this battery empty? Absolutely not. Is that a brick in there? Assuredly not. In fact, if these two batteries are also mobile phone batteries, then their capacity size or can be compared with the MAH. But if they are not of the same type, such a direct comparison might be wrong. Aren't they all lithium batteries? Isn't it all the same? Why not? Although the same is a lithium battery, in fact, the voltage of the two batteries is not the same, that is, because of the voltage, so simply than the size of the MAH number is not comparable. Generally speaking, the physical meaning of battery capacity refers to how much charge the battery can hold or release. We often use Ah(ampere hour) or mAh(milliampere hour) to express it. According to the definition of current: I=Q/ T, we can know that Q=It. The unit of current I is mA(milliampere), and T stands for time, unit hour(hour). Therefore, our battery capacity unit is mAh. That is to say, if a battery has a capacity of 1000mAh, and if it is operating at a current of 100mA, it can theoretically supply power for 10 hours. However, we can see from the formula that Q= IT does not take into account the voltage, so this unit only tells us how much coulomb of charge can be held inside the cell. But it doesn't say how much work the battery can do or what the maximum power the battery can provide. Different types of products have different operating voltages. So it's common to see a number in Wh next to the mAh. The work that the battery can do W=UIt=UQ, the unit of voltage U * current I is W(watts), so the W in the battery is expressed by Wh, which indicates how much work the battery can do. WH is a quantity directly proportional to voltage, current and time. MAH is usually used as an indicator of battery charge and discharge. It is an indicator directly proportional to the charge (discharge) current and time of the battery. To make it comparable to WH or convertible, we must also know the voltage of the battery. Simply put, Wh=mAh/1000* voltage. The voltage of the 6600mAh battery mentioned above is 14.4V, 14.4*6600=95.04Wh, so the work that can be done by his total release is 6.6*14.4*3600=342144 joules. And the general mobile phone voltage is 3.7, so the above 5200mAh mobile power supply can theoretically do 3.7*5200= 19.24Wh, 3.7*5.2*3600=69264 joules. We all understand this comparison, so we must pay attention to the voltage when buying lithium ion batteries in the future, oh, don't be fooled by big data!