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AT&T To Replace 17,000 Batteries
An anonymous reader writes "After four fires in two years — see earlier Slashdot discussions for background — AT&T is going against its own independent lab findings and declaring that the Avestor batteries powering its U-verse network aren't safe and need to be replaced. This is the network that SBC was building out prior to acquiring AT&T. Following the latest broadband equipment cabinet explosion in Wisconsin, the carrier says it will swap out 17,000 batteries deployed in several states across its network."
Any time you store that much power in a confined space, you're taking a risk. If anything shorts out one of those batteries, whatever shorts it out will go up in flames because the battery dumps so much current through it. Usually, these fires are caused by an internal short triggered by dendrite growth, random metal fragments, impact, or chemical breakdown of the separator. When this happens, the little bit of shorting metal gets extremely hot. This starts a chain reaction, known as a thermal runaway in which the increase in temperature causes an increase in the chemical reactions in the battery, which, in turn, causes an increase in temperature.
http://ecsmeet3.peerx-press.org/ms_files/ecsmeet3/2007/01/03/00002421/00/2421_0_art_0_jbbdol.pdf
http://en.wikipedia.org/wiki/Lithium_ion_battery
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several years ago, i had a job where we installed batteries in telecom shelters for Qwest, AT&T, etc. it was lead-acid batteries at the time. some of the guys were working on production, but even on hourly pay, there's still a lot of pressure to do the work in a timely manner. and invariably, the things get busted up. it may have happened during shipping, or during assembly. maybe the guys putting putting the connections on overtorqued them. maybe it was even a factory defect. but whoever is at fault, it inevitably happens. with lead-acid batteries, it's often pretty obvious. you get a crack in a case, and the thing leaks all over the floor. we always carried baking soda with us for this reason. maybe with a lithium battery, the defects are just not immediately evident. but from what i've heard wrt to lithium batteries on hybrid vehicles, lithium is just hard to deal with. too much energy density makes for more mishaps, i guess.