recharging alkaline batteries - sci.electronics

Message from discussion recharging alkaline batteries

Gary Coffman

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More options Aug 21 1993, 2:23 pm

Newsgroups: sci.electronics

From: g...@ke4zv.uucp (Gary Coffman)

Date: Sat, 21 Aug 1993 17:30:03 GMT

Local: Sat, Aug 21 1993 1:30 pm

Subject: Re: recharging alkaline batteries

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In article <20...@pitt.UUCP> jam...@cs.pitt.edu (James C. Xi'an) writes:

>Hi,
> I apologize in advance if this is not the proper forum for this
>discussion:
> I recently caught a late-night infomercial hosted by Dick Clark
>about a recharger for common alkaline batteries. The claim was
>that the recharger not only recharges common alkaline batteries
>but also extend their lives by almost 10 times. Because this is
>not my field, this claim raised one question in my mind:
> How can one decrease the battery discharge rate from the norm?
>(I assume the capacitance of the battery is not changed after
>recharging.) Or, if the fact is that the battery makers do not
>charge the batteries up to their full capacities, and the recharger
>does; then what is the full capacity of the normal alkaline batteries?
> The recharger was said to be built by a Professor Pfeiffer(sp?) of
>McGill University of Canada. Can anyone up there verify this?

The alkaline battery uses a primary cell chemistry. It can't be
recharged in the manner of a secondary cell chemistry such as
lead-acid or NiCd because the reactions aren't reversible. What
this device actually attempts to do is *depolarize* the cell with
a small reverse current. This allows more of the primary chemicals
to react. It should more accurately be called a *rejuvenator* rather
than a recharger.

A primary cell generates current by *irreversibly* consuming
it's reactants. Because of certain subtleties in the chemical
reaction paths, the surfaces of the reactants can become
passivated during discharge. This effectively stops the reactions,
and the electrical current production. "Long life" batteries
use an additional chemical in the cell to attempt to do much
the same depolarization without external current. By feeding a small
reverse current through the cell, however, it's often possible
to temporarily strip this film off the reactants much more
effectively and allow the reactions to continue for a while
longer. That's what the Buddy-L does.

The infomercial was vague to the point of deception about this
as can be seen by your confusion about the unit *both* recharging
the cells *and* extending their lives by almost ten times. That's
not what the fine print in the disclaimer actually says. What it
does is *depolarize* the cell up to ten times allowing you to use
up more of the reactants in the cell. There's a very real danger
here of letting the reaction eat through the outer casing, one
of the reactants, by this life extension technique. That will
release corrosive chemicals into your equipment. That's one of
the reasons that battery manufacturers caution you not to
attempt to "recharge" primary cells. The other is risk of
explosion since primary cells *can't* be recharged and can
get very hot and build up high gas pressures if reverse currents
are forced into the cell. The Buddy-L minimizes this risk by
limiting current flow to a very low value.

The Buddy-L is not worthless for certain types of primary cells,
but the infomercial is very deceptive in it's presentation. It
is *not* a charger in the technical sense.

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