[PLUG] Phone battery drain

Keith Lofstrom keithl at gate.kl-ic.com
Thu Nov 22 14:04:20 PST 2012

On Wed, Nov 21, 2012 at 05:09:47PM -0800, John Jason Jordan wrote:
> My Samsung Galaxy S2 battery has suddenly started draining within a
> couple of hours, even with no phone usage. I have several suggestions
> from Phandroid forums to try, but one of them seemed a good idea even
> if it is not the source of the problem, that is, clean the USB jack on
> the bottom of the phone. 

While cleaning the USB jack has a small probability of helping,
there are two more likely causes:  Battery failure, and radio
failure in the phone.

I just replaced the battery in my semi-dumb Nokia flip phone,
which used to last a week on a charge (not suprising with 10
calls a month) and recently dropped to a day.  The replacement
worked.  The replacement battery was from a spare/identical
Nokia that I keep around "just in case".  I ordered another
battery via Amazon for $4.

There is a grimmer possibility, a bit technical.  A high
quality cell phone (which nobody makes anymore) would use
a gallium arsenide power amplifier on the radio.  GaAs is
a faster process, so the amplifier does not need to be
pushed as hard to deliver both efficiency and reliability.  

But standard CMOS silicon is cheaper than GaAs, because 99%
of all integrated circuits are made with silicon, and most
of those are CMOS silicon.  Most of the phone is CMOS
silicon, which is great for the processors and memory and
such.  So to save a few pennies per phone, manufacturers
make the power amplifier with CMOS, too.

Whether you use the phone for calls or not, the phone frequently
sends out "registration requests" to cell towers to let the
network know where it is.  If the tower is distant, or you are
in a shielded area, the phone pumps up the transmit power of 
the registration request until the tower hears it.  That means
battery drain, but mostly it means increased stress on the power
amplifier.  If the shielding is a nearby metal table, or other
materials that interfere with the efficiency of the antenna, 
that maximizes the stress.  The stresses can damage transistors
in the CMOS power amplifier, causing them to leak current, even
when the phone is not transmitting.  This leakage can drain
batteries rapidly.  And the power amplifier can't be repaired.

A clever engineer can design a power amplifier, even a CMOS one,
to protect itself from this.  However, few engineers are that
clever, and the ones who are clever usually work for companies
that prefer you buy a new phone every year.  

Until customers make robustness a priority when buying phones,
demand long warranties, and support review sites that do reverse
engineering teardowns and reliability evaluations, the phones
will fail sooner and sooner, because the manufacturers compete
on price and features, not quality.  I'm not holding my breath
for improvements - just buying spares of products that seem 
relatively robust.  

So - good luck on the USB thing, but hope it is the battery, and
that you can get inside to replace it.  Otherwise, assume your
smart phone is more durable than kleenex, less durable than a
hanky.  Try not to put it antenna-side down on metal surfaces.


Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993

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