N900 Hardware Power Consumption

This page contains information on the amount of energy used by each subsystem of the N900, and where applicable ways it can be reduced.

Much of any reduction will require additional software, some may be possible by altering user behavior in ways that do not impact the users overall experience..

Measuring power usage is hard. For example, power consumption of the speakers/speaker-amp has to be disentangled from power consumption of reading a file from SD/eMMC, decoding it, PulseAudio's power use, and the DAC power use.

Below currents are from l3/l4 manual - assumed to be from a supply at 5 V.

  • FMTX 19 mA - l3/4
  • WLAN on - no powersave - 200 mA
  • WLAN transmit 802.11b - 150 mA

Battery parameters can be monitored thru fuel gauge asic TI BQ27200 [1]


Some preliminary numbers using the battery monitor chip.

These numbers are biased, and represent best cases. Some have had outliers which may be normal and unavoidable current spikes removed. This is under the assumption that the minimal power represents the minimum power achievable, and it should long-term be possible to - possibly with software patches - achieve these. +x indicates the measurement is for that element only. A raw measurement has no +, and is a total. Unless otherwise mentioned, numbers are for the idle locked case, with screen off. Assume

  • Suspend (echo mem >/sys/power/state), wifi and GSM off. 2 mA
  • Suspend, GSM on, connected to 3G (2 bars) 5 mA
  • Suspend, GSM on, connected to 2G. (2 bars) 3.6 mA
  • Idle, no SIM, wlan off 7 mA@4.1 V
  • Wifi on with maximum powersaving. +~2 mA
  • MMC card in. Under 1 mA
  • Xchat running, sporadic traffic. +8 mA
  • Screen on, no backlight. +80 mA
  • Backlight on max +150 mA
  • Media player playing MP3, one step above mute. 110 mA
  • Vibrator at max +100 mA
  • md5sum /dev/zero 250 mA
  • md5sum /dev/mmcblk1p1 - 1G SD card. 240 mA
  • md5sum /dev/mmcblk0 - internal MMC 240 mA (these indicate the CPU is somewhat idle, waiting on IO, and this counteracts any increased power use by the memory)
  • camera active, showing preview. (backlight off) 210 mA
  • GPS - location test gui - in continuous GPS recieve mode - +50-80 mA
  • 3G connected, good signal, no data or other activity +8 mA.
  • 2G connected, good signal, no data or other activity +5 mA

2G data, short pings

  • 1 s ping 130 mA
  • 10 s ping 70 mA
  • 30 s ping 45 mA

3.5G data, short pings

  • 1 s 186 mA
  • 10 s 120 mA approx.
  • 30 s 136 mA

3.5g data, long pings (8000 bytes)

  • 1 s 240 mA
  • 10 s 205 mA
  • 30 s 120 mA

2G data, long pings (8000 bytes) (with specified seconds between pings)

  • 1 s 160 mA
  • 10 s 105 mA
  • 30 s 50 mA

3G sending file at 150 k/s 375 mA 3G recieving at 200 k/s 275 mA

-- random adds:

WLAN PS-mode medium,10 mW, ssh login active, local xterm with bq27200 script loop -9, screen blanked, aggressive custom breathing indicator light: 20 mA


Many software subsystems interact to aim to reduce battery usage.