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Hang On For A Sec...
Before building a battery extender, there are a few things you
need to do first. Let's see what they are.
Read, read, read!
Yeah, before you do anything, first read up on as many battery
extender guides as you can find. You can check out
the edited versions of Dennis
Wolfe's excellent 'Build a battery extender' guide at Brighthand
and Pocket PC Passion. Brighthand
also has an article on how to build a better looking battery
extender. No matter what you read on each site, check out the
guides on the other sites for extra tips and information. It
always pays to dig further, as you will see momentarily.
Here are the direct links to the articles I mentioned :-
Check the voltages
Next, before you even set out to buy the parts, check
the voltage requirements of your Pocket PC. Also note the voltage
output of the AC/DC adapter that came with your Pocket PC. This is
very important. Even though most, if not all, Pocket PCs come with
internal voltage regulators, you wouldn't want to turning your
Pocket PC into a really expensive paper weight, would you?
To check the voltage requirement of your Pocket PC, turn it
over and look for a label like this :-
This is the picture of a label on the back of my Casio E-115
Pocket PC. Look closely at the lower portion. It states that it
requires a DC input of 3.7V but needs only 3V to
run. The higher DC input is needed to charge the internal battery,
which on closer inspection (read = on removing the battery
cover) is a 3.7V Li-Ion battery. No surprise there.
But why do they use a 3.7V battery when the Pocket PC only
needs 3V? Well, while the Li-Ion battery may start out with 3.7V
fully charged, its voltage does not remain at 3.7V all throughout
its use. The voltage actually drops as it is being used. The more
current is drawn (when using CompactFlash cards or playing
movies), the faster the voltage will drop. Behind the scene, the
Pocket PC's internal voltage regulator converts the higher voltage
to the constant 3V needed by the Pocket PC. So, by using a 3.7V
battery, the battery will be able to power the Pocket PC for a
certain period of time before its voltage drops below 3V.
So, what happens when the battery drops below 3V? Will it still
power the Pocket PC? You will be surprised but yes, the battery
will still power the Pocket PC. In fact, it will do so until its
voltage drops to about 1.8V. This is because the internal voltage
regulator boosts the voltage up to 3V but this draws a lot of extra
current in the process. So, as the voltage keeps dropping below
3V, the current draw increases exponentially (which in turn causes
the voltage to drop even more!).
Next, take a look at the AC/DC adapter that came with your
Pocket PC. This adapter converts AC (alternating current) power to
the DC (direct current) power which your Pocket PC needs. Check
its output voltage. My E-115's adapter is able to provide up to 2A
of current at 5V to the Pocket PC.
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