Wednesday, 9 February 2011

Wifi battery drain on CM6.1.1 on my HTC Desire

I (only) recently upgraded from CyanogenMod 6.0.0-RC1 to 6.1.1, and started noticing much higher battery drain, just like others did as soon as it came out. Aside from a subjective feeling that the battery drains fast, the proportion of time spent running "Android OS" under "Battery use" and the proportion of "Time spent without sleeping" under "Spare Parts -> Battery history -> Running" seemed high:

There's been some discussion by other Desire owners on CyanogenMod forums and on XDA Developers over whether the "Wi-Fi sleep policy" is better set to "Never" or "When screen turns off"; it certainly seems intuitive that the latter would save more power. Being the scientific sort I experimented, running on "When screen turns off" overnight and on "Never" from when I woke up (always within range of my router):

"Never" is clearly much kinder to the battery on my phone, at least on CM 6.1.1 and within range of my router. Another subjective observation: I'm not sure whether it's just a change in power accounting, but with "Never" I now find "Wi-Fi" accounts for a much larger proportion of "Battery use" than it used to even though the rate of power drain seems to be back to normal.

I generated the graph from data captured and exported by Battery Graph, using GnuPlot (though perhaps just screenshotting the one Battery Graph made would be easier!):

set term png
set xlabel "Clock time"
set ylabel "Charge (%)"
set timefmt x "%s"
set xdata time
set xrange ["`gdate -d "2011-02-09 00:45" +%s`":"`gdate -d "2011-02-09 15:00" +%s`"]
set arrow \
from "`gdate -d "2011-02-09 08:01" +%s`", graph 0 \
to "`gdate -d "2011-02-09 08:01" +%s`", graph 1 \
nohead \
linetype 0
set label '"Wi-Fi sleep policy" set to "Never"' \
at "`gdate -d "2011-02-09 08:01" +%s`", graph 0.5 \
center \
set datafile separator ","
set output "battery.png"
plot "battery_graph_Feb09-002305_to_Feb09-150905.csv" \
using 2:3 \
notitle \
with lines \
smooth bezier

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