# Computing journey time from the battery percentage in Tesla electric vehicles

The tesla model S electric vehicle is available with battery pack having an energy capacity of 90kWh. During a journey through an urban environment the average power demanded by the motors is 7.1kW, and the average energy conversion efficiency is 80%. Calculate the journey time (in min) if the energy stored in the battery pack falls from 60% at the start of the journey to 47% of the capacity at the end of the journey

How is the answer 79?

## 1 Answer

The total energy spent during the journeyis

\[(60/100-47/100)\times 90= 11.7 \text{kWh}. \]

Since the conversion efficiency is 80 %, the effective energy available is

\[80/100 \times (11.7)=9.36 \text{kWh}.\]

Since the average power demand is 7.1kW, the journey time is

\[\frac{9.36}{7.1}=1.3183 \ \ \text{hours}=1.3183 \times 60 =79.0985 \approx 79 \text{minutes}.\]

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