Power Hacks

Without power, even the best GPS receiver is nothing more than just an interesting box that does nothing. Given that a GPS unit has to pick up signals from satellites that orbit the globe at an

altitude of 12,000 miles (19,200 km) and complete two rotations around the Earth every day, it’s easy to see why there is a fair amount of power drain

by the antenna in order to pick up and decode the signal. Add to that the power load of processing the data and displaying it, and you see that two or four small batteries aren’t going to last too long under these conditions.

This chapter describes some power hacks you can do to your GPS to improve battery life, and how to extend battery life by making use of external sources.

GPS devices that contain a rechargeable Lithium-Ion battery are appearing on the market now. While this is generally an advantage, it can also be a disadvantage if it runs out in the field and you don’t have access to a suitable charger.

GPS Power Needs

On the whole, battery lifetimes aren’t that bad, depending on what batteries you use. Most GPS receivers use either AA or AAA batteries, but not all AA or AAA batteries are created equal, as you’ll see in the following sections.

For more information on batteries, a good website to visit is http://michaelbluejay.com/batteries.

Alkaline Batteries

A fresh set of alkaline AA batteries (see Figure 3-1) in a receiver such as the basic Garmin eTrex will last approximately 22 hours, while the top of the range eTrex (the Vista) will go through the same two AA batteries in about 12 hours.

chapter

in this chapter

˛GPS power needs

˛Portable 12-volt supply

˛Portable battery packs

˛Alternative power sources

42 Part I — Hardware Hacks

FIGURE 3-1: AA alkaline batteries

Use poorer quality alkaline batteries and you will see a drop of a few hours in these times. If you try using cheaper zinc-carbon batteries, you will see a huge decline in battery lifespan. A set of AAs might last only a few hours.

In high-drain devices (which a GPS receiver most certainly is) cheap zinc-carbon batteries are a false economy and offer very poor performance.

Compared to other types of batteries, alkaline batteries have greater availability, are reasonably priced, and have a consistent lifespan (when using good brands). They often have a warranty against leakage and damage, and are packaged with expiration dates (again, when using good brands). However, they are costly, have a short lifespan, and are wasteful (not to mention environmentally unsound).

Lithium Batteries

If you are willing to spend more and get a set of lithium AA batteries (not to be confused with rechargeable ones), as shown in Figure 3-2, you will see a huge increase in battery life (two or four times what you get from alkaline AA batteries). However, these batteries can cost two to four times as much as good quality alkaline batteries.

Chapter 3 — Power Hacks 43

FIGURE 3-2: AA lithium batteries

Lithium batteries have an excellent lifespan in use, and a very long shelf-life. They also offer excellent cold weather performance, and are lighter than alkaline or rechargeable batteries. However, they’re generally not widely available; and as mentioned above, they are very expensive.

Rechargeable (NiMH) Batteries

By far, the best way to invest your money is on rechargeable batteries. Get the best possible batteries, which means choosing nickel-metal hydride batteries (NiMH), shown in Figure 3-3, rather than the older and inferior nickel-cadmium (NiCd) batteries. In addition, choose the batteries with the greatest capacity (over 2000 mAh, preferably 2300 mAh or greater). The rule is that the greater the mAh (milliamp hour) capacity, the longer the batteries will last. These batteries will initially be more costly than alkaline batteries — especially if you figure in the cost of the charger too — but they can be recharged hundreds, if not thousands, of times.

Although some systems on the market claim to be able to recharge ordinary alkaline batteries, I don’t recommend them. They are not recommended by battery makers; and not only do they invalidate any warranty on the battery (such as the leakage warranty), but they also increase the risk of the battery damaging your device. Play it safe and get proper rechargeable batteries and chargers.

44 Part I — Hardware Hacks

FIGURE 3-3: NiMH rechargeable batteries

Compared to other types of batteries, rechargeables have a good lifespan in use, and can be recharged repeatedly. They’re environmentally friendly, and you can recharge them while you’re on the move, using in-car chargers or solar chargers.

Some drawbacks to rechargeable batteries are that they are not widely available and they are very costly. They generally have a shorter life than alkaline batteries, and they don’t handle cold weather as well as alkaline or lithium batteries. They also require recharging before first use, which can be inconvenient. Finally, some rechargeable batteries can be slightly smaller (in length) than alkaline batteries, which can make the device cut out if subjected to shock or vibration.

You should be sure to get two chargers. Get a fast charger for when you want batteries in a hurry (see Figure 3-4), and get a slower charger that you can use occasionally to recharge and recondition your batteries. Alternating between a fast charger and a slow charger is good for battery health and will guarantee you the best performance and lifespan from your batteries.

Make sure that your charger matches your batteries. Never use a charger that’s not designed for the batteries you are charging.

Chapter 3 — Power Hacks 45

FIGURE 3-4: A fast battery charger that you can power from a wall socket or from a cigarette lighter socket in a car

For best performance and safety, never mix battery types. That includes mixing old and new batteries, different brands, and different types or capacities of rechargeable batteries. Mixing batteries can result in poorer performance and reduced lifespan, and creates a real risk of batteries exploding or rupturing.

A super battery-saving tip is to check the settings of your GPS. Look for an option or mode called Battery Saver or Low Power Mode. Not all receivers have this setting, but if yours does, it means that your GPS receiver consumes less power than normal, enabling it to last longer on a set of batteries than it typically would. The disadvantage of this setting is a slight decrease in accuracy because of the way in which the unit keeps a lock on the GPS satellites.

As for battery brands, there are plenty of good ones — Duracell, Energizer, Sanyo, Hama and Ansmann are all of excellent quality and backed by good warranties. Avoid buying cheap “no name” generic batteries, or batteries that are loose or out of blister packs — if these are DOA or leak all over your device, you are unlikely to have any warranty to fall back on.

Another thing to remember is that some GPS receivers contain a small button cell, similar to a watch backup battery (usually non-user replaceable), that is used to store some data in memory in case the main batteries are depleted or removed. However, if you store your GPS for a long period of time without batteries or with dead batteries, this can cause a drain of the backup