Data Hacking

Chapter 3 — Power Hacks
These small lead-acid batteries are extremely handy auxiliary power packs and keep their
charge for a long time in storage (recharge them every three months when not in use). A
sticker on the side of the battery (see Figure 3-7) is ideal for keeping track of charge dates!
Lead-Acid Battery
Charge history
Last charge . . . / . . . / . . .
Next charge . . . / . . . / . . .
FIGURE 3-7: Suggested information to keep
on the battery
When you are outdoors, take great care when carrying a lead-acid battery. Any damage or
crack in the battery will leak dangerous, corrosive sulphuric acid.
If you want an alternative to lead-acid batteries, the following section describes how you can
make simple battery packs from ordinary batteries (or rechargeable batteries).
Battery Packs
Making a battery pack isn’t hard. All you need is a holder for the batteries and some way to
wire that to the GPS you use. The easiest way to wire it up is through the GPS connector.
Before continuing, however, first a little battery theory. If you take two AA batteries and put
them in a circuit end to end (see Figure 3-8), the voltage will equal 1.5 volts plus 1.5 volts,
resulting in 3 volts.
3V
+ − + −
FIGURE 3-8: Two AA batteries end to end provide 3 volts
This is called putting the batteries in series. However, if you place the batteries in parallel, that
is, take a wire and connect them positive to positive and take another wire and connect that
negative to negative (see Figure 3-9), and then measure the voltage across the two wires, you
will get a voltage measurement of 1.5 volts.
49