Hack6.Upgrade Your Car Battery

Hack 6. Upgrade Your Car Battery

If you want to add a lot of electrical devices to your vehicle and still be able to start it up and drive it, you may need to upgrade your car battery.

There are two primary competing purposes for the battery in a vehicle:

To provide a very high-amperage output for several seconds to start the car, then allow the engine to generate any further needed electricity.
To provide a medium- to low-amperage output for many hours when the vehicle is off, to power devices such as car alarms or the station preset memory in car radios.

To meet these two different needs, two types of batteries are used in automotive applications: conventional lead-acid and deep-cycle.

If you are familiar with laptop or mobile phone batteries using nickel cadmium, nickel-metal hydride, or lithium ion, you know that they are designed to be completely discharged and recharged many times. Conventional automobile batteries use lead-acid and are designed to put out a large current (to start the car) for a short time, and then be recharged after only a shallow discharge. If you completely discharge your automobile battery (say, by leaving all the lights on for several weeks) you are likely to severely limit the life of the battery.

Recreational vehicles (RVs) often have two batteriesone starting battery with its good starting characteristics, and one deep-cycle battery designed to put out a lower amperage for a long time and to survive deep discharge.

In addition to the starting and deep-cycle qualifiers, a few other measurements are used to compare batteries:

Cranking amps (CAs): This is the maximum output amperage the battery can sustain for 30 seconds (i.e., to start the car). A good battery can put out 1 kiloamp (1000A) for about 30 seconds before the voltage starts to sag. Since cold weather makes batteries very tired, another necessary comparison is cold cranking amps (CCAs), which are how many amps the battery can sustain for 30 seconds in cold weather. This number will be lower than the CAsfor instance, in the 800A range. Bigger engines (with more cylinders) and diesel engines require higher CAs or CCAs to start in warm or cold weather (respectively). In warm climates, CCAs don't matter much; in cold climates, this becomes an important measurementdon't underrate your battery if you want your car to start in the winter. The two measurements aren't quite interchangeable, but they're roughly proportional; a high-CCA battery is generally a high-CA battery, and CCAs are always lower than CAs.
Reserve capacity (RC) and amp-hours (Ah): Both of these terms describe how long a battery can put out a lower number of amps. Reserve capacity describes how many minutes the battery can put out 25A before the voltage goes too low. Amp-hours are defined for much lower currents, and usually specify how many amps the battery can put out for 20 hours before the voltage drops.

1.7.1. Convenient Power Connectors

One benefit of a battery upgrade is that you can get one with a dual-post configuration. Some vehicles have posts on top of the battery, and the battery connectors bolt around these posts. Some batteries have sockets on the side that you screw battery connectors onto. If you purchase a battery that has both, like the one in Figure 1-15, you can use the unused set to cleanly run thick wires to the trunk of your vehicle. For more on how to hook these up, see "Gauge Your Wires" [Hack #3].

1.7.2. The Hack: Installing a Deep-Cycle Battery

If you are installing many gadgets in your vehicle, you will be most impacted by the amp-hours the battery provides. Most likely, you will be tapping the battery for only 510A, or perhaps more amps if you run your stereo at full blast for a long time while the car is off.

As mentioned earlier, a deep-cycle battery is designed for applications where there is a long time between vehicle starts, or where the battery does a lot of work while the vehicle is off (i.e., when it's not being charged). The latter situation is what we're trying to address.

Figure 1-15. A car battery with both kinds of connectors (posts and sockets)

Although deep-cycle batteries are not as good at starting, this is where the CCA and CA ratings come in. If you overcompensate with the cranking amps, you should be able to install a deep-cycle battery and have it consistently start your car, while still being resilient to the constant device draw of all your gadgets.

In your search for a suitable deep-cycle battery, you will probably encounter hybrid deep-cycle and starting batteries, or possibly marine batteries. Marine batteries are designed to deal with months of not starting and still put out a starting current; they also are designed to deal with the vibration and rocking that occurs on a boat. These features are unlikely to be of benefit to you if you have decent suspension on your car, don't go off roading, and drive your car frequently. However, a hybrid might be a good way to split the difference if you're in a cold climate and are concerned that a normal deep-cycle battery won't have enough power to start your car in freezing weather.

Optima (http://www.optimabatteries.com) makes a series of battery upgrades that are extremely popular in competition cars. Their Yellow Top series, in particular, is designed to take heat, vibration, and deep discharges with minimal capacity loss (see Figure 1-15).

When you purchase your new battery, get the largest unit that will fit in the space you have and that has greater CCAs and CAs than your existing battery (assuming your existing battery is the correct one for the vehicle and successfully starts your car). Any auto shop should be able to look up your vehicle in its database and tell you what shape and kind of battery you need.

Swapping your starting battery for a deep-cycle battery will give your car a lot more electrical staying power with the simplest installation. But if you really need to run devices for a while when your car is off and you don't want to ever risk needing a jump start, you should consider a dual-battery setup [Hack #10].