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From: graham@arcturus.uucp (Graham;Thomas D.)
Newsgroups: sci.electronics
Subject: battery back-up
Message-ID: <1991May14.154859.21874@arcturus.uucp>
Date: 14 May 91 15:48:59 GMT
Distribution: usa
Organization: Rockwell International
Lines: 15


 Got a question re using lead-acid, car battery, as power supply for
 house alarm system.  I'm using a Delco 40 month rated about 20 hrs (?).
 A typical auto 12v battery.  I keep it on a floating charge at about 
 13v, from a cheap  little battery charger.  I wanted to check its
 power reserve/capacity, even though the little green ball indicated
 full charge, so I discharged it at 4 amps rate.  In a little over an
 hour the voltage had fell to 9 volts.  YET, the green ball was still
 indicating full charge.  Is something wrong with this picture???
 Is keeping the battery on a charger, at 13 volts, the proper way to
 maintain it???   Should it be charge/discharged cycled???
 Also, it has a sealed (?) top so you can't check the electrolyte level
 or add water.  (But it is probably OK since the green ball looks near 
 the top).  Any help appreciated, thanks.  Tom Graham.