Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!usc!wuarchive!decwrl!hayes.fai.alaska.edu!accuvax.nwu.edu!nucsrl!telecom-request From: rpw3%rigden.wpd@sgi.com (Rob Warnock) Newsgroups: comp.dcom.telecom Subject: Re: Nicad "Memory" Message-ID: <9888@accuvax.nwu.edu> Date: 19 Jul 90 06:19:24 GMT Sender: news@accuvax.nwu.edu Reply-To: Rob Warnock Organization: Silicon Graphics Inc., Mountain View, CA Lines: 39 Approved: Telecom@eecs.nwu.edu X-Submissions-To: telecom@eecs.nwu.edu X-Administrivia-To: telecom-request@eecs.nwu.edu X-Telecom-Digest: Volume 10, Issue 498, Message 1 of 10 In article <9807@accuvax.nwu.edu> forrette@sim.berkeley.edu (Steve Forrette) writes: | Can someone recap the discussion of "memory" in nicad batteries? I'm | having a problem with my HT5300 AT&T cordless phone. I had it | unplugged for about two months, and like a dummy didn't disconnect the | battery in the handset. So, I assume that it was on standby (since it | was off the base for awhile), and totally discharged the battery. This is not the "memory effect" (which is something completely different), but a case of your causing a "cell reversal". When you completely discharge a multi-cell NiCd battery, *some* cell is going to go all the way to zero volts first, and then as the other cells continue discharging they're going to back-bias the one that zeroed first, and start charging it "the wrong way". | This is bad news, right? Yup! The reverse current causes chemical changes in the cell which can permanently damage it. Among other things, rumor has it that conductive "whiskers" grow across the cell. There is urban legend to the effect that you can cure a back-biased NiCd cell by zapping it with a very strong (but brief!) forward charging current (as from a large capacitor), supposedly to "blow the whiskers", but as I said, I consider this in the urban legend category. | It's been charging for over two days, and | reads only 2.65 volts. The battery is rated at 3.6V, 720mAh. When I | take the handset off the base, the LO BATTERY light comes on, and none | of the keys do anything. Any thoughts? I think you need a new battery. Sorry. Rob Warnock, MS-9U/510 rpw3@sgi.com rpw3@pei.com Silicon Graphics, Inc. (415)335-1673 Protocol Engines, Inc. 2011 N. Shoreline Blvd. Mountain View, CA 94039-7311