Display article   Subject:  Battery Use on Portable Computers
   04/30/97   18:33:01


BATTERY USE ON LAPTOP AND NOTEBOOK COMPUTERS

Introduction

Even though battery powered devices have been around for many
years, it still seems that we continually question why they act
the way they do.  Batteries in laptop and notebook computers are
no exception to the rule.

"Why doesn't my battery last for the {insert your own time} that
your catalog says it will?"  We've heard this question in the
stores, so we'll try to provide an answer.  To begin, we will
list the types of batteries used in Tandy laptops/notebooks, list
some of the "published" times on our computers and give you some
explanation of how those figures are determined, how they apply
to the average user, and then some tips on getting the maximum
from a battery.


Types of Batteries

There are two basic types of batteries -- `lead acid' and
`Ni-cad.'  The Tandy 1100 FD and the Tandy 2800 HD use the lead
acid type.  This is a sealed battery quite similar in some
respects to the battery in your car.  The balance of our
notebook/laptop line uses Ni-cad batteries.  The Tandy 1400
laptops used standard Ni-cad technology, with the 1500 HD and the
2810 HD using high capacity Ni-cad.

During the early years of laptop computer development, standard
Ni-cad technology offered the user the ability to use their
batteries over and over again instead of having to throw them
away each time and buy new batteries.  Ni-Cad offered the maximum
economical power.  It did, however, have one major drawback that
became evident very quickly with laptop computer users -- "the
dreaded MEMORY CHARGE disease."

Now it's not fair to blame the spread of this disease entirely on
the battery -- the laptop user must share some of the blame.  And
also the laptop itself is partly to blame.  Most users "forget"
to remove their battery when they plug in the AC adapter.  Most
users will use their laptop batteries for 10-20 minutes during
the day, then plug them in to charge when they get back to the
office or home that evening.  Others quickly remove and change
batteries at the very first warning beep that the battery is
getting low.

Ni-cad batteries MUST be discharged completely before they are
recharged.  And this is even more important with the high
capacity batteries like those used in the Tandy 1500 HD and
2810 HD.  This means completely discharged, not just half way, or
down to the first warning that the battery is low.  The prudent
user will make sure to leave their computer on until it runs out
of battery power at least once a week before recharging the
battery.  In so doing, the user prevents a `memory charge' from
building in the battery.  For those of you that do not know what
this means -- if you use a Ni-cad for only 1/4 of its charge and
recharge it, and do this several times in a row, the battery will
soon memorize that this is all the power you want and will only
charge to 1/4 of its power.

So -- if a battery develops this "MEMORY CHARGE DISEASE," is it
curable?  In most cases the answer is YES -- it may take a few
complete discharges (called DEEP DISCHARGES) before the memory
goes away and the battery once again starts taking a full charge.
If you suspect you have MEMORY CHARGE DISEASE, leave your
computer on overnight or during the day until the battery goes
dead, then completely recharge it.  Then repeat this sequence six
times in a row.  In most cases the full charge capability will
return.

Another important point to remember with laptop Ni-cad batteries
is that they can be recharged about 400 times over their life.
And the more times a battery is recharged, the less capacity it
will have.  As the battery gets closer to the 400 charge number,
it will be down to approximately half its charge capacity as
compared to when it was new.  Remember this when you know your
battery USED to give you 3 hours of life but now only gives you
about 1 hour of life.

Many people cannot understand why their laptop battery should be
any different from the battery in their portable drill, or their
portable electric razor, or some other tool:  "My razor lasted
four years before I had to replace it -- why did my laptop
battery only last nine months?"  The two are similar yet very
different when it comes to the battery.  Your razor, for example,
takes very little power to run and can use the battery down to
very little charge.

Your computer, on the other hand, is probably used every day for
a couple of hours, recharged and used some more and recharged
again, and it takes a tremendous amount of power to spin up the
hard drive.  And of course the battery probably remains in the
unit when used on AC which means the battery is getting charged
when it really doesn't need to be.

If you do some quick math -- the razor gets charged 30-50 times a
year -- and the laptop gets charged about 400 times a year.  Most
people become concerned when they see battery life starting to
drop off, which usually happens as the battery approaches the
250-300 charge mark.  Your initial response is "my razor didn't
do that!"  But the truth is that your razor probably did do that
-- you just can't remember because 4 years ago it went two weeks
between charges and now it only goes one week between charges.
And you really don't even notice when it does or when it doesn't
because all you do is put it in its charger stand every morning
and the charger stand takes care of when it gets charged.


Battery Life of Specific Laptops

Battery life that a user can expect to get from their unit will
vary tremendously from user to user.  And the `published' battery
life times of the early laptop computers was computed differently
than it is now computed for computers like today's Tandy 2810 HD.
At the time of the 1400 LT laptop, what few laptops there were in
the industry simply measured battery life based on 10% floppy
disk usage, without any activity during non-floppy usage.
Whether right or wrong, it was the way the industry chose to
measure it.  In keeping with the industry, Radio Shack measured
its early laptops the same way.  It is extremely important to
remember that these times are with a fully charged, new battery.

Tandy  1400 LT -- 4 hours

This `published' time was based on floppy disk use 10% of the
time.  A more practical time value for this unit (with 10% floppy
disk use and and an actual program running during non-floppy
access) would be TWO HOURS.

Tandy 1400 LT with the 20 MB hard disk drive kit:  No battery
life was ever published for this upgrade, but one could expect
only about 30 MINUTES of use.

Tandy 1400 FD -- 4 hours

Once again, this time was based on 10% floppy disk usage and
running at 4.77 MHz.  A more practical time value for this unit
(with 10% floppy disk use and and an actual program running
during non-floppy access) would be 2 1/4 HOURS or just slightly
better than the 1400 LT.  Battery technology hadn't changed much
between these units, but it was slightly more efficient.

Tandy 1400 HD -- 2 hours

Once again, this time was based on 10% disk drive usage of the
FDD only.  A more practical time value for this unit (with 10%
hard drive use, no floppy use, and and an actual program running
during non-hard drive access) would be 45 MINUTES.

Between the time of the 1400 series and the 1100 FD, the industry
had gone through some changes in how battery life was measured.
When the industry was using straight computer-on time with 10%
disk access as a measurement, they found that the times were just
too far off from what the user was really getting.  In keeping
with the industry, Radio Shack also changed its method of
computing battery life.  Although this method was still not
perfect, it did more closely resemble what the user could expect.
(You'll read later on how this once again changed at Radio
Shack.)

Tandy 1100 FD -- 5 hours

This time was based on 1% floppy disk usage with the LCD being on
90% of the time.  Most users and magazines are reporting anywhere
from 3 1/2 to 4 1/2 hours of usage depending on how much the
floppy disk drive is used.  Since the 1100 FD has DOS and
DeskMate in ROM, you can see where little floppy disk usage is
required for the DeskMate user.  Those users that run
applications from diskette will be the ones that get 3 1/2 to 4
hours of battery life.

Tandy 2800 HD -- 2 hours

This time was based on 1% hard disk usage, no floppy disk usage,
LCD brightness at its lowest setting, LCD on 90% of the time, and
all power management modes set to on.  In actual use, average
users are reporting three quarters to a full hour of actual use.

Between the units above and the 1500 HD, Radio Shack decided to
use a more realistic number when determining battery life.  It
was determined that the user actually used their hard drive about
10% of the time instead of only 1% of the time.  So Radio Shack
adopted a measuring system of 10% HDD use, 1% floppy use, LCD on
90%, brightness at minimum setting, serial ports turned off, no
printer port activity, no upgrade memory installed, no modem
installed, and all power management functions enabled.  While
this formula does not fit every user's habits, it more closely
defines practical use of a laptop in a mobile environment.

Tandy 1500 HD -- 4 hours with a new battery.

Tandy 2810 HD -- 3 1/2 hours with a new battery.

With the Tandy 1500 HD and the Tandy 2810 HD, there are some
simple rules that MUST be followed by the user to obtain maximum
battery life.  And there are several things the user can do to
extend their battery life.  First, to obtain the times listed
above, the user must have turned on all the power savings modes
of his unit.  With the SETUPxxx program furnished with each of
the computers, the user can control all the various settings.
For instance, on the 2810 HD, POWER MANAGEMENT must be set to ON,
the hard disk drive should be set to turn off after 1/4 minute,
the display and standby times should be set to the lowest limits
that the user can function with.  The LCD brightness switch must
be set to its minimum setting, as this one setting can affect the
life by 20-30 minutes when set to high.


Hints and Tips

There are several other tricks a user can do to maximize battery
life:

1. If nothing is used in the serial port connector -- turn it off
with the SETUPxxx program.

2. If the program being used does not require fast number
crunching (like database entry, word processing, note taking,
etc.), consider setting the speed of the processor to its slow
setting.  This can be done either in the SETUPxxx program or
straight from the keyboard by pressing <FN>+<F3> while running
most programs.  Note the power light will change to amber when
the processor is in slow speed.  Pressing <FN>+<F3> again will
toggle it back to fast.  [Author's Note: I am writing this
article using a Tandy 2810 HD and DeskMate Text on a plane bound
for sunny California and I need maximum battery life, so I have
put the processor in slow mode since the computer is waiting for
me to type on the keyboard -- not me waiting on the computer.  I
expect to get all the way to California on one battery
(approximately 3 1/2 hours flying time).]

3. Set the LCD brightness to minimum.  Even here on the plane
with the sunlight coming in the window, this setting gives more
than sufficient lighting to see the screen.

4. Take the battery out of the computer when it is not in use.
Now this might sound silly, but even when the computer is turned
off it still uses battery power.  Why?  Because the power switch
is actually an electrical switch and power is always being used
to monitor whether the switch has been pushed or not.  This is
true on the 1500 HD and the 2810 HD.  Even with a fully charged
battery and the computer turned off, the main battery will
completely discharge in approximately eleven days.  So it makes
sense to remove the battery until it is needed.

5. Use the RESUME feature of the 2810 HD only when it is
absolutely necessary.  If battery life is your main concern, turn
off RESUME from the SETUPxxx program.  When RESUME is enabled,
the separate RESUME Ni-cad battery is constantly being charged by
the main Ni-cad battery.  And after the RESUME Ni-cad has used
all its power, the RESUME function automatically changes over to
the main Ni-cad for its power.  Therefore, it is possible for the
user to shut off their system with RESUME activated and the main
battery system will discharge in a matter of one or two days if
there is 5 MB of memory in the machine.

6. Remove the battery from the unit when it is being used on AC
current, unless charging is taking place.  This prevents the
Ni-cad batteries from developing a memory charge.  Also note that
the majority of the power savings modes are disabled when the
unit is plugged into AC current.

Things to remember:

1.  adding memory upgrades will decrease battery life

2.  adding a modem will decrease battery life

3.  using a printer will decrease battery life

4.  setting brightness of the LCD to maximum will decrease
battery life

5.  using programs that are hard drive intensive will decrease
battery life
