Data Hacking

Chapter 3 — Power Hacks
As you can see, a typical alkaline D-cell battery has approximately six to eight times the capacity
of a AA NiMH battery. The disadvantage is one of weight — twelve AAA batteries weigh
about the same as one D-cell, but the D-cell has 14 times the capacity.
Now that NiMH AA batteries are capable of capacities of 2500 mAh, they are getting close to
the capacities of their alkaline rivals.
What You Need
This section describes what you need to build a battery pack. Remember that there are many
ways to build one and the final pack can be of any shape. The only important caveat is that you
don’t subject the GPS unit to too much voltage; if you stick to the normal battery voltages
you’ll be fine.
For example, a Garmin eTrex has two AA batteries and therefore runs at 3 volts, while a
Garmin GPS III+ runs on four AA batteries, providing the operating voltage of 6 volts.
Feeding more voltage through the GPS than it needs serves no purpose. If you feed it only what
it needs, you avoid wasting batteries (and carrying extra weight), and supplying wasted additional
voltage.
Batteries
A good battery to use is the AA battery because it is quite light and easily available. If you want
greater capacity, then you might want to consider using D-cells, which have a far greater lifespan
but are heavier to carry.
Battery Holder
Battery holders can be almost anything that can hold a battery. You can use a specific battery
box (available from electronic outlets), a box you have lying around your home or office that
you wire up, or something that you may already own that holds batteries.
A good example of something that already has a battery inside is a flashlight. Moreover, a
flashlight has the added advantage of having a ready-made switch (although you may want to
wire in a different switch because you might not want the flashlight on when you are running
your GPS from the batteries).
Wiring and Connections
Figuring out the wiring and connections isn’t hard if you follow the instructions in Chapter 2.
All you need to do is hook up a connector suited to your GPS to a length of wire (covered in
Chapter 2) and solder that wire to the connection in your battery pack, paying special attention
to ensuring that you connect the positive and negative terminals correctly (see Figure 3-11).
Load the holder with batteries and away you go!
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