[Tfug] Source for notebook batteries?

[Bexley Hall]

Hi Jim,

> First, a terminology issue.  Each "cell" of a multi-cell pack is
> capable of acting as an independent battery on it's own, in a
> flashlight or something.

That's only because of the vernacular use of the term "battery"
to be synonymous with "cell" (as most "batteries" that were
used in the past were single cells -- AA, AAA, C, D, etc.
N.B. a 9V battery is *really* a "battery" as it has 6 cells 
within it)

Wikipedia says:
   'The name "battery" was coined by Benjamin Franklin for an 
   arrangement of multiple Leyden jars (an early type of capacitor)
   after a battery of cannon.  Strictly, a battery is a collection
   of two or more cells, but in popular usage battery often refers
   to a single electrical cell.'
When speaking formally about these things, cell and battery
have very definite meanings.

> Therefore it's not improper to refer to each
> "cell" unit as a battery as I've done at times.

It's imprecise and leads to the ambiguities you see when 
trying to explain the composition of a *battery* (multi-cell
collection) without having to add parenthetical qualifiers
wach time you use the term "battery" (does he mean multiple
cells or just one of the cells used to make up that 'battery'?)

> Second, if you're replacing only SOME "cells" in a multi-cell pack,
> you're doing it wrong.  Chain a weaker battery in series with a
> stronger one and you run several risks - at a minimum you
> won't get full performance out of the new battery(s).  You also
> don't have the opportunity to replace, say, 2400mAh batteries 
> with 2600 or 3000 rated, which IS possible if you replace them 
> all at once.

You are assuming batteries (collections of cells) have a single
"atomic" chain of cells within them.  This is often not the
case.

I've disassembled battery packs (see how often ambiguity creeps in?)
where there were three or more voltages supplied by the "battery"
to the laptop.  Since the manufacturer can design the battery
to any specifications he choses, you can cheat and reduce costs
in the laptop by providing these different "power supplies"
to the laptop instead of relying on voltage *converters* to
synthesize the various voltages from a *single* voltage delivered
by the battery.

So, you might have a string of two cells paralleled with two
*more* to provide a hefty "low voltage" for use by the logic
crcuits in the laptop while another three cells sit on *top*
(in series) with those 2x2 to provide a higher voltage to
power the laptop's backlight inverters (having a higher
working voltage on the input to the inverter allows for
greater efficiency as there are less switching losses,
relatively speaking).

There's *lots* of BFM involved in the design of batteries
(collections of cells), their chargers, etc.  Manufacturers
typically have data *books* for each cell chemistry as the
rules that apply to one chemistry don't necessarily apply
to other chemistries.  Hence my caution that they are NOT
as innocuous as the might appear to be ("These ain't
yer granpa's 'batteries' no mo'e!")

--don