Battery knowledge: the difference between mAh and Wh

　　One of the major factors restricting the development of smart phones is the battery. For so many years, it can be said that the battery of mobile phones has been stagnant. The performance of mobile phones has improved, but there is still no good solution for the battery life. Because of this, the mobile power market is so hot. But for those who buy mobile power, they don’t even know the unit of battery capacity. They may even mistakenly think that a 6000mAh mobile phone battery is better than a 5600mAh laptop battery.

　　One time my friend looked at the camera battery on my desk and said, "Your camera battery is so much bigger than my power bank, how come its capacity is only a little bit bigger?" As shown in the picture above, the power bank on the left is 5200mAh, while the big camera battery on the right is only 6600mAh.

　　In terms of volume, the lithium battery on the right is at least twice as big as the one on the left, but judging by the numbers, the 6600 is definitely not twice as big as the 5200. Is this battery empty? Absolutely not. Is there a brick inside? Definitely not.

　　In fact, if these two batteries are both mobile phone batteries, their capacities can still be compared using mAh. But if they are not the same type of products, it may be wrong to compare them directly. Aren't they both lithium batteries? Aren't they all the same? Why can't they be compared? Although they are both lithium batteries, careful friends will notice that the voltages of these two batteries are actually different. That is, due to the voltage, simply comparing the mAh numbers is not comparable.

　　The Lenovo laptop battery in the picture below is only 5600mAh, which is not as good as three Xiaomi batteries.

　　In simple terms, 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), t represents time, the unit is hour, so our battery capacity unit is mAh.

　　That is to say, if the capacity of a battery is 1000mAh and the current when it is working is 100mA, it can theoretically provide power for 10 hours.

　　However, we can see from the formula that Q=It, and the voltage is not involved, so this unit can only indicate how many coulombs of charge can be held inside the battery. But it cannot indicate how much work this battery can do, and what is the maximum power the battery can provide. The working voltage of different types of products is different. Therefore, we often see a number in Wh next to mAh. The work that the battery can do W=UIt=UQ, the unit of voltage U * current I is W (watt), so the W in the battery is expressed in Wh, which indicates how much work the battery can do.

　　The voltage of the 6600mAh battery mentioned above is 14.4V, 14.4*6600=95.04Wh, so the total work it can do is 6.6*14.4*3600=342144 joules.

　　The voltage of a general mobile phone is 3.7, so the work that the 5200mAh mobile power bank above can theoretically do is 3.7*5200=19.24WH, 3.7*5.2＊3600=69264 joules.

　　Wh is a quantity that is proportional to voltage, current, and time. mAh is usually used as an indicator of battery charging and discharging. It is an indicator that is proportional to the battery's charging (discharging) current and time. To make it comparable or convertible with Wh, the battery voltage must also be known. Simply put, Wh=mAh/1000*voltage.