Question on cell phone batteries

[chuddachudda]

Is there a known mechanism by which holding a cell phone in your hands could cause the batteries to apparently have an increase in charge?

This "increase in charge" is indicated by the "battery life indicator" going up from say one bar to two, or two bars to three.

The cell phone starts out at room temperature, which according to what I've been able to find on the internet is the optimum operating temperature for cell phone batteries. Device is probably warmed a bit by hands (that's the only physical effect I can think of), and then returns to room temperature after being held in hands for a few minutes, but the apparently increased charge persists for half an hour or more (as indicated by the "battery life indicator" display).

I'm not making a claim of having witnessed a paranormal event, but this is something I saw demonstrated twice by the same person over the weekend and I don't have an explanation for it. The person stated that their intention was to partially recharge the cell phones, and according to the battery life indicators the person was successful on two tries out of three. I haven't been able to replicate this on my own, nor have others who tried (as far as I know), so I haven't been able to dismiss this as attributable to merely warming the battery a bit.

If any of you can help me out here, or point me in the direction of someone who can, I'd appreciate it. Anybody know someone who designs cell phones?

Thanks.

edit: Maybe this is the wrong forum, I don't know. If it is, tell me where it should go.

[JoeEllison]

I don't know about that... what I DO know is that increased heat seems to prevent full charging. My air conditioning went out this past July. I live in Florida, so it was more than an inconvenience. It took two weeks to get the part delivered and installed, and in the meanwhile my phone, and my wife's phone, simply would not hold a charge. Usually, I'm good for 3-4 days if I'm not using the phone heavily, but during my time without AC it went down to about 36 hours. As soon as we got the AC fixed, the phones went back to normal usage.

[Freethinker]

The indicator on a cell phone isn't a good indication of the state of charge of the battery. It simply monitors the voltage output of the battery, which is a function of power demand. Power demand in a cell phone varies with signal strength. Warming a lithium battery lowers it's internal resistance, which increases its output voltage.

[PB2007]

How many of use have tried the trick of taking dead batteries out of a device (TV remote usually) and rubbing them in your hands for a minute? Suddenly the batteries come back to life! Zombie batteries?? :D

I have a digital thermometer outside which relays the temperature back to a base station indoors. Last night and this morning when the temperature dropped below 2 C the low battery icon lit up. Now at 9 C the low battery icon is unlit.

Even a few degrees temperature change can affect battery performance.

You can also find the same effect (increased battery status bars) just by switching a phone off and on again.

As stated above "The indicator on a cell phone isn't a good indication of the state of charge of the battery." Really you need to measure the voltage properly to see whats happening.

[krelnik]

Depending on what chemistry is used in the battery, it can be very difficult to have an accurate battery gauge. On some chemistries you can measure voltage, which drops as capacity is used up. But often the drop is not linear, and you have to do some math to get the gauge right. On other chemistries (such as NiCd), voltage does not drop significantly until the cell is near empty, so you have to be more clever.

And, there's always the possibility that the phone is lying to you. Consider this post on the Good Experience blog (http://www.goodexperience.com/blog/archives/010155.php) from the just other day.

Like the battery indicator, the signal strength on a cell phone is deliberately weighted toward the high end. I worked on a phone development project several years ago. When the first units went to the carrier for approval, their first request was to toss the perfectly calibrated battery indicator in favor of one that sat at 4 bars for around 75 percent of the charge.

Other commenters on that post indicate that a considerable amount of work can go into calibrating the battery indicator, which is a further testament to how hard it can be to get it right.

--Tim Farley

[LTC8K6]

Batteries also normally recover some voltage after the load is removed from them.

Carl Tilley used this to scam people into believing that batteries in his electric cars were being recharged from his magic box. He would set up his initial measurements right after a run, and then wait a few minutes and read the higher voltage, then ohh and ahh over the "free electricity", and collect the donations.

[chuddachudda]

Thank you all for your replies, you have been very helpful.

chuddachudda