# Battery Capacity vs Load approximation

This is a simplified battery capacity calculator for Li-polymer, Li-ion batteries to estimate the needed battery capacity if you have known load currents. You need to know: a. Time needed to run your loads in hours; b. Load currents in Amps.

Calculator works the following way:

Current 1 is ONLY for LOW currents, when I(currents) are less then the approximate size of the battery. Time t1 is the accumulated time that Current 1 was ON. This is the main load current. without high pic loads.

Current 2 is ONLY for HIGH currents, when currents are greater then the approximate battery size. Time t2 is the accumulated time when the Current 2 was on.This is the time when you have high loads for short times.

Please run first approximation and after that if the result for Capacity is greater then Current1, the result is approximately valid. If the result is much less then the Current 1, please disregard the result and use High load Current 2 (without entering anything in Current 1 and Time 1 slots)

Note1: Time t2 has to be less then 0.1, otherwise the result will be very far off the reality.

Note2: This is just an approximation to give you an idea for approximate size of the battery. Real results can be influenced by many factors. Please see the forum discussion or information articles.

Please note 1Ah=1000mAh and 1A=1000mA.This valculator uses Amps, but it would work in mA too, just the result will be in mAh

Here we say that at 3V Li-polymer or Li-ion practically have no charge left. Even at 3.2V battery considered fully discharged. So we recommend to cut off load before 3.2V. Good rules for the designer to leave about 10% battery capaciy left. This will extend battery life. At 3.5V batery have around 3% capacity.

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