From: chrz@tellabs.com (Peter Chrzanowski)
Subject: Re: rechargeable batteries
Organization: Tellabs, Inc.
Date: Tue, 15 Dec 1992 23:38:11 GMT

In article <1gl2e1INNn0u@moe.ksu.ksu.edu>, zchen@phys.ksu.edu (Zheng Chen) writes:
> In article <1992Dec15.082507.21066@netcom.com> royg@netcom.com (Roy H. Gordon) writes:
> >This must be a FAQ.
> >
> >Having just purchased a portable CD player that runs on 4 AA batteries,
> >I now want to acquire rechargeables.
> >
> >Preferably, I'd like those that don't have a memory, that you don't have
> >to wait until they're nearly drained to recharge them.
> >
> >Is this possible?  Can I use any type of rechargeables?  What are my
> >choices and what is recommended?
> >
> >Thanks in advance.
> >
> >				-- Roy
> 
> 
> I think that nowadays all the rechargables will not retain their memory.
> So you don't have to worry about when to refresh them. When I purchased
> some rechargables with the charger, I was instructed to leave a pair
> in the charger all the time. If these batteries have memory, a power
> outrage will make these batteries unusable.

Depending on how much current the charger supplies, leaving them in all
the time may overcharge them -- which *can* damage them, esp. a fast-charger
that's not smart enough to know when the batteries are fully charged.

> 
> But there is one more problem. All the rechargables have 1.25 volt instead
> of 1.5 volt. I have no problem with my walkman because it takes only two
> AAs. Now for a CD player, it requires four AA to get 6 volt. If you use
> the rechargables, you only add up to 5 volt. Will that make any difference.

An alkaline throwaway battery will output 1.5 volts WHEN NEW into an open
circuit; under load the output will be less.  If this battery is discharged
at a constant rate, its output will fall in a roughly linear fashion to
about 0.7 volts, at which point it will abruptly drop to zero.

Because the output voltage of a throwaway battery drops as it is used up,
most electronic equipment that runs on such batteries is designed to work
down to at least 0.9 volts per cell -- otherwise users would be discarding
batteries that still had quite a bit of energy in them.

Nickel-Cadmium rechargeables produce 1.21 volts per cell when fully charged
and about 1.18 volts just before they're entirely discharged; they also
have a lower series resistance than alkaline throwaways and so their output
voltage will drop less under load.  Thus, the output voltage of a NiCad,
unlike a throwaway, remains almost constant until the charge is all gone.

The bottom line is that NiCads can almost always be used to replace throwaway
alkalines; their lower voltage is rarely a problem (it seems to be a problem
in many infrared 1 remote controls, however).  

Because NiCads don't get weaker as throwaways do, they give no warning that
they're about to poop out.  Also, a fully charged NiCad only holds about 30 
percent as much energy as a new AA throwaway alkaline.  They're certainly 
cheaper to use (calculate cost per kwh of electricity in throwaway batteries!).  

My rechargeable batteries  have lasted for years.

> I haven't tried this yet. My CD player is still on his way.
> 
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