You may think the A in mAh looks weird. So do I.
However, the A is capitalized because A is for “ampere” in the Units International System. And mAh is short for “milliampere-hour.”
According to the evolution formula of Ohm’s law under the pure resistance circuit, we know I=Q/t (current=electric charge/time). So Q=I*t. That’s why the battery capacity unit is Ah or mAh. It is a simple way of estimating battery life in hours.
In other words, if a battery capacity is 1000mAh and the working current is 100mA, it can theoretically last for 10 hours.
But it is only the guideline of what you can expect to see in the ideal condition. In the real world, it will be with power loss. We have covered the topic in the last article.
Although mAh is the right unit to estimate the amount of energy that battery can hold, the different batteries may have different voltages. Then how can we compare?
For example, there are 2 things here. One is a 3.7V2000mAh battery, and the other one is a 14.4V2000mAh battery pack. So if these are both 2Ah batteries, do they both hold the same amount of energy?
Of course not! The 3.7V battery will theoretically deliver 2amps for one hour, with the voltage around 3.7V. The 14.4V battery pack will also theoretically provide 2amps for one hour, but with the voltage around 14.4V. So one way we can compare the stored energy of these 2 batteries is to use another unit called watt-hour. And Wh is the abbreviation for it.
Volts*amps=watts. So you can get that volts*amp-hours=watt-hours. Then the single cell has a capacity of 7.4Wh, and the battery pack has a capacity of 28.8Wh.
Now you can know which battery stores more energy because we compare apples to apples and watt-hours to watt-hours.
Knowing the mAh and Wh is essential. It will help you get the right battery according to your demands. Also, there is a regulation that all batteries over 100Wh are not allowed on commercial flights. So you’d better know the information on this topic.