9 Volt Battery Life Calculation

Thread Starter

ElectricalCollegeStudent

Joined Apr 13, 2018
2
Hey guys,

I'm working on an Arduino project and trying to calculate the battery life (dissipation) of my power source. I would like to know if there is a calculation to determine the battery life that if possible, also incorporates the operating power variable.

The discharge bar graph listed on the data sheet is from 9 volts 4.8 volts so it doesn't really help as my minimum voltage to power circuit is 7.2V; since power is not dissipated linearly.

I have done testing and gathered the information below. If you need any more information please let me know. I have timed the battery life with a stopwatch and it was approximately two hours.

Details are as follows:

Battery Details

9 Volt Energizer Battery (datasheet attached)
Nominal (full) Voltage of battery = 9.6V

Circuit Details
Continuous current drawn= 128mA
Operating Current Variable (3 second intervals)=336mA
Minimum Voltage (with 9.6V Battery) to operate circuit= 7.2V

Thanks for your help, much appreciated.
 

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crutschow

Joined Mar 14, 2008
34,284
If you look at the Toy graph the average current form 9V to 7V is about 7.8v/270Ω = 28.9mA.
The time to reach 7.2V is 12 hours, giving a battery capacity of 347mAH
That means the life would be about 347mAh / 120mA = 2.9 hours for your steady load.

To include the momentary load of 336mA, you need to know how often that 3 second load occurs.
 

Hymie

Joined Mar 30, 2018
1,277
Note: Circuit is operating at room temperature
There is not sufficient information within your data and/or the battery specification to give a definitive answer.

From the manufacturers spec. it is clear that the battery capacity is reduced at higher loads – your circuit is drawing more than 100mA (the maximum shown on the spec sheet), albeit not at a constant drain.

I would argue that your real-life test of approximately 2 hours (for your circuit) is as good as any calculation might give.

One final thought, you might be able to prolong the battery life by regulating the battery voltage to say 7.5V, thereby reducing the battery drain current (that would otherwise be drawn by the circuit at higher input voltages).
 

DickCappels

Joined Aug 21, 2008
10,152
Battery life is very dependent upon the conditions of operation and in many cases the starting condition of the batteries. If the batteries were in a hot warehouse for a year or two before getting to you, your results may be far different.

The most satisfying way that I have found is to find the curve closest my application and then make an estimate based on that curve and what my application needs.

Another way is to run down a few batteries in your circuit and then come up with minimum and mean battery life.
 

MrChips

Joined Oct 2, 2009
30,712
PP3 9V battery is not meant to deliver high current. Typical capacity is 550mAh.
C/10 discharge rate would be 55mA for 10 hours.

If you need more than 20mA you are using the wrong battery.
Consider that a 9V battery in a smoke detector will run for more than 1 year.
 
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