Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!ll-xn!ames!amdahl!nsc!gates
From: gates@nsc.nsc.com (Tim Gates)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Overcharging NiCad batteries?
Keywords: NiCad rechargeable batteries, laptops, foreign power
Message-ID: <6625@nsc.nsc.com>
Date: 27 Sep 88 20:03:25 GMT
References: <3008@dalcs.UUCP>
Reply-To: gates@nsc.UUCP (Tim Gates)
Organization: National Semiconductor, Sunnyvale, CA. (Mesa Group)
Lines: 27

NiCad batteries have something called Memory.  This is when the
battery is partially discharged then recharged many times.  The
battery then begins to act as if it can only store a small amount
of energy (the normal discharge amount).

The storage capacity of the battery can be restored by FULLY
discharging the battery, then fully charging it.  This should be
repeated 3 or more times.  Each time you will increase the storage
capacity of the battery.

To fully discharge the battery, just leave the computer turned on
until it is dead, then connect a low value (2 to 5 Ohms) resistor across
the battery terminals for several hours.  I suggest that a high wattage
resistor be used (3 times the expected power dissapation).

If you are concerned about data integrity when the battery is low,
use only the resistor to discharge the battery.  This will take longer.
Allow 3 hours for each amp/hour of capacity for which the battery is rated.

If you are interested in other NiCad battery problems and their
solutions,  send me mail.  If there is enough interest, I will post.

-- 
Tim Gates
National Semiconductor
{amdahl|decwrl|hplabs|nscpdc|pyramid|sun|voder}!nsc!gates
"Where the men are men, and the computers run scared."