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Razor Battery Bug?

  1. Nov 30, 2006 #1


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    Staff: Mentor

    Razr Battery Bug?

    My electrical engineering is a little thin, so bear with me...

    A bunch of my friends and coworkers have Motorolla Razr phones that have absolutely atrocious battery life - single-digit hours. Part of the problem may be how often it powers-up to search for a tower in low coverage areas, but today I ran a voltmeter across several of the batteries and found something interesting:

    The battery is a 3.6v, 700mAh LiIion with four terminals on it. Checking a near-dead battery (according to the phone) with a voltmeter showed that there are 3 negative terminals and 1 positive one. The voltages were something like 3.8, 3.8, and 1.1V. On one that has the same battery life issue but just came off a charger, they were all like 3.9V.

    So it seems to me that the phones are only using one cell of a 3 cell battery! Since I think it is unlikely that the phone is physically wired wrong, I'm thinking maybe it is supposed to switch between cells, but there is a software bug that prevents it from doing that. Looking online, it looks like they don't publish release notes, so I can't find that out, but they do have updates and I'll try that....

    ....Failing that, I was thinking of using a thin piece of wire to bridge 3 of the leads on the phone to combine the cells of the battery in parallel. Whatdaya think?

    One concern I have is doing that when the one cell is low - could that damage the battery if the voltages aren't matched?
    Last edited: Nov 30, 2006
  2. jcsd
  3. Nov 30, 2006 #2
    It is possible that the cells were poorly chosen and the trigger to switch cells (if that is in fact the case) is unable to operate due to unsuitable terms, i.e. too low of a voltage drop being produced in a time too fast to switch cells. Although that sounds incredible stupid coming from a major manufacturer. I don't use batteries that much so my knowledge of what could be wrong is limited.
  4. Nov 30, 2006 #3
    Possible reason for defective Lithium batteries at wiki, don't know if it applies to the cell phone batteries tho,

    "Internal contaminants inside the cells can defeat these safety devices. The mid-2006 recall of 10 million Sony batteries used in Dell, Apple, Lenovo/IBM, Panasonic, Toshiba, Hitachi, Fujitsu and Sharp laptops was a consequence of internal contamination with metal particles. Under some circumstances, these can pierce the separator, rapidly converting all of the energy in the cell to heat"


    Even though, you are reading 3.8 volts on the other 2 cells, it doesn't mean they are fully charged. Try connecting a resistor to the other cells and see if you get a significant voltgate drop. If so they are dead as well.

    There is a very efficient switching voltage regulator built inside every cell phone, that strives to save every single amp.

    A third possibily is that one cell is used for the cpu, the others are used for the transmitter/receiver and standby. It's hard to say without schematics.
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