Surely this has happened to you before. When faced with the possibility of buying a device, we look at the battery capacity. It is also possible that, seeing that it is a high number, we think that it is a "great battery". But did you know that battery life depends not only on its capacity, but also on its consumption?
Let's explain it easy: let's suppose we have a phone with a 2000mAh battery (milliamps per hour) which is equivalent to 2A (Amps).
With measuring instruments, we can verify that this particular phone has a consumption, watching videos non-stop, of 500mAh. Now, if the maximum capacity is 2000mA per hour, and watching videos consumes a quarter of its capacity, it means that in 4 hours it will be completely discharged.
On the other hand, let's put a hypothetical and exaggerated case of a "super battery!" of 6000mAh, but the phone consumes watching videos about 6000m. How long will it last? 1 hour. A super battery, but it lasts less than the previous case that had 3 times less capacity.
So, although the capacity is important, the consumption is also important.
In conclusion, to calculate the battery life, you need to have 2 pieces of information: capacity and consumption.