[Nexus S General] bedalus:
Miscellaneous

[Q] You claim you cannot increase battery life using UV beyond 2%. Justify yourself!

[A] When the processor is in use (i.e. not asleep or idle) UV does save a tiny amount of power. I tested with the most extreme UV my phone could handle. With a high performance governor, e.g. smartassv2, extreme UV would reduce CPU drain by 13%, or about 7 mA. With a governor that keeps the CPU frequency low, CPU drain would be reduced by about 18%, or 4.6 mA (weighted - see the spreadsheet starting cell H88).

Remember, these savings are limited to the processor, and only when it is active. For most users, this will mean the screen is on. For comparison, the screen on minimum brightness displaying black uses 9mA. On max brightness, displaying white, it uses 690mA. Let us assume some median value, ~350 mA.

A saving of 4.6 mA out of at least 350 mA (screen) plus 20 mA (CPU)

= 1.2%

A saving of 7 mA out of at least 350 mA (screen) plus 50 mA (CPU)

= 1.8%

So, regardless of your choice of governor, even with extreme undervolting, you are not going to be able to increase your battery life by more than 2%.

Articles and Documents

Diane Hackborn's article on the formula that produces the dodgy Android OS usage statistic in the battery menu:

https://plus.google.com/105051985738280261832/posts/FV3LVtdVxPT

(note, this bug is fixed as of Android 4.0.4)

Data sheet for the fuel gauge chip:

http://www.maxim-ic.com/datasheet/index.mvp/id/6621

Link to great article on SOC (State of Charge) http://www.mpoweruk.com/soc.htm >>> explains all the reasons why I don't trust battery monitor widget and the phone's own battery stats.

Great article on the difficulties of accurate metering (thanks aLNG):

http://low-powerwireless.com/blog/d...t-schemes-for-battery-powered-devices-part-1/

In the article DUT stands for Device Under Test

The implication is that DMM [Digital Multi Meter] voltage drop readings (to measure amps) take hundreds of milliseconds, a will miss instantaneous battery savings above this time window. However, I am using an analogue meter, the the needle responds to all current. Due to the mass of the needle, there is inertia to overcome, which provides a form of averaging.

Quote from the article:

"a GSM cell phone can have current pulses of 2 amperes that last approximately 500μs while the power amplifier is on and transmitting, and then drop back down to the milliampere level for the remainder of the 4.5 ms GSM cycle."

500μs is 0.5ms, so is 1 tenth of the 5ms GSM cycle. 2 amps at 1/10th of 5ms = average of 200 mA

When I ran the test with my equipment, GSM broadcasting uses at least 170 mA - see row 36. I think this is a nice proof that the analogue multimeter beats the digital multimeter hands down for dynamic amps (i.e. changes happening below the millisecond level.) I'm also very satisfied that my result is close to the result stipulated by the article. It improves faith that my readings are accurate.

[Q] What could add inaccuracy to the readings?

[A] The dBm scale assumes a resistance of 600 ohms, but the resistor has 3% accuracy which means it could be as high as 618 ohms, or as low as 584 ohms.

[A] Also, the scale is very small, so I've read the needle to the nearest fifth of a dB

Other articles (thanks aLNG)

A study of the mA drain of various components of a smartphone

http://www.usenix.org/event/atc10/te...rs/Carroll.pdf

An ARM presentation on unifying power management procedures in the kernel

http://elinux.org/images/0/09/Elce11_pieralisi.pdf