On Mon, Jan 18, 2010 at 2:22 AM, Daniel Dalton <d.dal...@iinet.net.au>
wrote:
[snip]
I want something with really good battery life, perhaps
5 hours or more.
This is where life becomes complicated. A factor which you need to
consider is useful battery lifetime (as opposed to battery capacity,
which determines computer running time).
A typical rechargeable battery (including lithium ion) can provide in
the range of 300 to 1000 full charge-discharge cycles. After this, you
either must replace the battery or else run the computer on the AC adapter.
Battery availability limits your options:
=> Laptop manufacturers thus far have failed to standardize
batteries. So if you purchase a FooBar model A101 today and go
shopping six months later for a second laptop, you likely shall
discover that the FooBar model A101 no longer is made, and that
the FooBar Model 201 uses a different and incompatible battery.
Laptop manufactures obviously assume that the useful life of a
laptop computer is no more than a year or two or three. Of
course, considering the problem of electro-migration, this may
not be unrealistic. (An integrated circuit self-destructs as it
is used, due to a process not unlike that of electo-plating.
Recent devices with extremely narrow conductor widths and spacing
do not last as long as earlier devices. The reduced geometry
allows smaller die sizes and thus lower cost.)
=> Moreover, if you have a FooBar machine, you likely shall discover
that no other brand of machine uses the same battery.
=> If, six months or a year after your purchase of the FooBar
model A101, you discover a dealer who has a stock of batteries
for the machine, the batteries may be past their useful life,
even though the batteries are unused and have been stored
properly (see below).
You may be able to find a custom battery shop which can disassemble the
battery pack of your FooBar model A101 and rebuild it with fresh cells.
Still another factor which must be considered is that, with lithium ion
technology, it may be futile for you to purchase a spare battery pack.
This is because a lithium ion cell begins aging the moment it is
manufactured. Within two or three years (sometimes less), the cell
loses its ability to hold a charge, irrespective of usage.
=> Nonetheless, a spare battery pack does give you a housing into
which a custom battery shop can build a new battery for you.
=> Also, with heavy usage, each spare battery provides another 300
to 1000 charge/discharge cycles; but to take full advantage of
this, you need a means for charging the battery outside of the
computer.
=> Again, if you get a spare battery, don't leave it unused on the
shelf, because by the time the original battery fails, the spare
is going to be near the end of its useful life.
Thus, to extend the useful "running-on-battery" lifetime of a laptop
computer, two things would be helpful: (1) standardization of the
battery packs which mount in or attach to the computer, and (2)
provision for plugging in a power cable from an external battery pack.
RLH
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