I wonder calculation of the battery life, depends of its voltage level. Basic calculation of battery life is given below:
Battery Life = Battery Capacity in mAh / Load Current in mAh
However in this formula we are not using any voltage levels. I know that formula is very basic formula, there has to be a constant (0.7 or 0.85), although we can't use any voltage level in this formulas. How we can read the datasheets to making exact calculation? For an example if I use 3.7 V battery, what is the lasting voltage? What if my limit is 2.7 V in my system, I mean that system will passive under 2.7 V, how will be the calculation? What if I use the limit as 2.4 V? In the basic calculation formula we couldn't use voltage level.
Best Answer
Determining the remaining battery charge (State of Charge) from its voltage is tricky; the discharge curves aren't straight lines, and for some chemistries, the first part of the discharge curve is very flat and this makes the battery voltage almost independent of the battery's charge level.
Also, the discharge curves vary depending on temperature, age, and load current.
You can get a very rough estimate of remaining charge looking at a battery's voltage at a known, constant discharge current by checking the discharge curves in the battery's documentation and implementing a calculation based on the linear part of the chosen curve (if any).
If you need a prediction of State of Charge that is more-or-less accurate, you can use a Fuel Gauge IC, which keeps track of "what goes in and what comes out" and derives a State of Charge from that.
This Application Note provides further reading, should you want any.