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## Data Logger Battery Life Calculator

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This calculator computes the estimated battery life of a data logger for a given sample rate, sensor power, number of sensors, and sensor on time per sample, and mA hours of the battery.

 Input: Battery Energy, E (mAh) Battery Voltage, V (V) Data Logger Power when Sleeping, Pl (mW) Sensor Power, Ps (mW) Sensor On time per sample, T. Enter 3600, if continuously powered. (seconds) Sample Rate, F. Enter 24, if continuously powered. (Samples per day) Number of Sensors, N Result: Energy usage per day, Ed (mAh/day) Estimated Battery Life, Life (Days)

If batteries are connected in parallel, their mAh is multiplied by the number of cells in parallel, but their voltage is the same. For example, four 1.5V AA batteries in parallel will have a voltage output of 1.5V and have 8000mA of energy.

If batteries are connected in series, their voltage is multiplied by the number of cells in series, but their mAh at the higher voltage is the same. For example, four 1.5V AA batteries in series will have a voltage output of 6V and have 2000mA at that voltage.

Common Battery Capacities:
9V Alkaline: 565 mAh
1.5V AA Alkaline: 2000mAh
1.5V C Alkaline: 7000mAh
1.5V DAlkaline: 20,000mAh

Equations:
Seconds per hour= 3600. 24 hours per day.

Current draw from logger without sensors, I(log)= Pl/V.

Current draw from all sensors when continuously powered: Is= Ps*N/V

Average current draw from all sensors when temporarly powered for T seconds before taking F samples over a 24 hour period:
Is(av)= Is*(F/24)*(T/3600);
Is(av)= (Ps*N/V)*(F/24)*(T/3600);

Total Average Current, I(av):
I(av)= Is +I(log),
I(av)= Ps*N/V*(F/24)*(T/3600) + Pl/V,

Battery Life (hours) = E(mAh)/I(av); (Assuming I(av) is in mA.)
Battery Life (hours) = E(mAh)/[Ps*N/V*(F/24)*(T/3600) + Pl/V].

Battery Life (days) = Battery Life (hours) / 24.

Battery Life (days) = E(mAh)/[Ps*N*F*T/(3600*V) + 24*Pl/V].

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