“Not sure how long my hero’s battery will last with GPS on and my phone vibrating every second to indicate if on right track!?!”
– This and similar concerns have frequently been expressed when I presented the PocketNavigator – a navigation system guiding pedestrians by vibration patterns instead of spoken turning instructions.
To quantify how much battery power is actually lost to constantly repeated vibration pulses, I tested the battery consumption of two different patterns in comparison to a non-vibrating phone.
In brief, in my setup, the vibration cost less than 5% of the battery life. As comparison: leaving the screen on will drain the phone’s battery in 2-3 hours. In consequence, instead of draining the battery fast, vibration can even help to save battery if it allows users to leave the screen turned off.
The apparatus created heartbeat-like vibration patterns, i.e. patters consisting of two pulses followed by a long pause. The apparatus was run three times. Each run used a different pulse length, i.e. 30 ms, 60 ms, and 0 ms (no vibration as baseline).
- 24.71 hours for 0 ms pulse length (baseline)
- 23.48 hours for 30 ms pulse lengths = 95.0 % of the baseline, and
- 23.48 hours for 60 ms pulse lengths = 95.0 % of the baseline.
Using linear approximation to account for the fact that the battery was never 100% charged when the trials commenced, we also calculated the trend lines (see Diagrams, used Excel’s linear approximation), which changes the prediction to
- 24.18 hours for 0 ms pulse length (baseline)
- 23.28 hours for 30 ms pulse lengths = 96.3 % of the baseline, and
- 23.60 hours for 60 ms pulse lengths = 97.6 % of the baseline.
Battery life in all cases was around 24 hours, sufficient for normal use. Constant vibration reduced battery life by 2.4 – 5.0 % minutes. Increasing the vibration length from 30 to 60ms per vibration pulse had no effect on battery life. As comparison, when the screen is constantly kept on, the battery drains within about 2-3 hours.
Hence, the additional battery loss is justifiable when considering that at the same time we gain the ability to continuously communicate information to the user. When using short vibration pulses, desigers do not even have to consider the effect of the pulses’ lenghts on battery life.
This data shows that the impact of having the phone emitting vibration pulses constantly is not very high.
This means that as means to constantly convey information, e.g. as navigation system that is supposed to convey information all the time, vibration has a much lower impact on battery life compared to the screen, which empties the battery in a few hours. On a Nexus One, vibration can allow to constantly convey information for almost 24 hours, enough for the typical smartphone user who has gotten used to charge the phone every night.