Storing Electricity for the Off-Season

Battery & Electrical Considerations

The conventional mindset would hold that when you put a vehicle away in storage, nothing really changes -- nothing should wear, degrade or otherwise decline in state from that which was present at the time it was last shut off. The reality is that the battery will gradually discharge even under the best of circumstances, moisture will seep its way into every conceivable electrical connection, and the gremlin of corrosion will add resistance to circuits that you'd never before considered! Integrating proper battery and electrical system care into the put-away routine is cheap insurance.

About Your Battery
The battery is really no more than a device that changes chemical energy into electrical energy. A healthy battery depends on continual replenishment from the alternator to keep the potential electrical energy in solution (in the sulfuric acid bath that resides within the each of the battery cells and between the positive and negative plates). During a discharge condition, a chemical reaction takes place in the electrolyte where the acid percentage becomes reduced (measured in terms of specific gravity of the battery electrolyte). This weakening of the solution causes sulfur ions in the solution to combine with lead plate materials, allowing for the formation of lead sulfate. To a certain point, recharging of the battery allows the lead sulfate to recombine into th e electrolyte, allowing the battery to recover. Beyond a certain point, however, a battery will become "sulfated" so badly that the active material will shed from the plate grids and the unit will be beyond recovery and will need to be replaced.

As a matter of fact, without any external influences a battery will lose about 1% of its charge per week at room temperature, a figure that increases substantially with ambient temperature increase. So, the first lesson in battery preservation is to maintain the state of charge so that the measured specific gravity is between 1.260 and 1.268. This can easily be measured with a syringe battery hygrometer. As an alternative to measuring specific gravity, the open circuit battery voltage (without any loads connected) can be checked with a common voltmeter. Open circuit battery voltage during storage should not fall under 12.2 volts DC. The Eastwood line of Battery Tender products are designed to apply an optimal amount of charging current to keep the unit within this desired state-of-charge.

With the significance of battery charge state clearly defined, it's important to add an understanding of the influence of temperature to battery longevity. This is particularly vital for vehicles that are stored outside or in unheated garages. While the high temperatures associated with summer driving and hot engine compartments can shorten battery life through electrolyte loss, the freezing temperatures of winter can cause the electrolyte to freeze, resulting in a swelled or cracked case and ultimately a ruined battery. Interestingly, the electrolyte in a fully charged battery won't freeze until -60°F, but that of a discharged battery may freeze at temperatures as high as 18° above zero. The lesson here again is that preserving a high state of battery charge will largely overcome the possibility of a battery freezing.

"Parasitic Draw"
Apart from the physical storage device (the battery) that we've been focusing on so far, what are some related electrical system negatives for which we should consider developing an ounce of prevention before put-away? One little-known concept is that of parasitic draw, a term that gets its name through the way it drains a battery's energy in the same way that a parasite insect would draw blood from a host animal. In the automotive sense, the parasite(s) are electrical consuming devices that remain "on" or in a state of readiness even when the vehicle is not turned on or running. These "parasites" have become much more numerous with the advent of electronic technology, running the range from stand-by functions on alarm systems to "keep alive" memories in powertrain control modules (PCM's). Parasitic draws siphon off the latent energy in a battery, accelerating the rate of discharge. Older vehicles without all the high technology systems are also susceptible to parasitic draws, but for very different and largely electro-mechanical reasons. Sometimes, for example, a diode in the pull-in winding side of relay may short, causing the relay coil to remain partially energized all the time. Even the diodes in an alternator can "leak", causing the battery to gradually discharge through the rotor winding over time. The most common cause for this sort of an electrical draw is a glove box or trunk lamp that remains on, resulting in the parasitic discharge.

So with all of these possibilities, how does one know if they are or will be afflicted with a parasitic draw problem before put-away, or should the resolve be to simply disconnect the battery from the electrical system every time the vehicle is parked? The best solution is to locate and eliminate the source of the draw before it ever becomes a problem. The test for this is surprisingly simple, and requires only a common digital volt-ohmmeter (DVOM) with capability of reading milliamps (thousandths of an ampere of current flow). To conduct the test first turn off the ignition, switch off the radio and any other power-consuming devices, and shut the vehicle doors to ensure that the interior lights don't add to a false reading. Now detach the positive battery cable, and with the meter in the mA range, touch one meter lead to the positive post of the battery and the other to the free end of the detached positive battery cable. This means that any battery current being used (parasitic draws) will be passing through the meter, which is connected in series with the hot side of the electrical system. A good rule-of-thumb is any more than about 20mA (.02 amps) indicates a parasitic loss (for non high-tech vehicles), or about 40mA for computer-controlled vehicles. So what do you do if you suspect that you have a parasitic draw…there must be about 1,000 places to look, right? To narrow your search and resolve the problem quickly, leave the meter connected as described and simply remove the fuses and relays one at a time while watching the meter reading. If the meter reading suddenly drops into the acceptable range, Viola! ...you've narrowed the offender to one circuit and one or two components.

Other Electrical Issues
With battery charge status ensured and any offending draws eliminated, what other preventable electrical maladies might be lying in wait when the car cover is pulled off in the spring? The last concept to touch upon here is galvanic corrosion and the voltage drop problems that may result from its untreated condition. Galvanic corrosion is an electrochemical reaction that takes place in the presence of moisture and a corrosive agent such as road salt. The observable outcome is increased electrical circuit resistance, most commonly afflicting the grounding points, harness connectors and places where dissimilar metals come into contact with one another. Think of the battery as a big water tower with the wiring being a series of pipes to carry the water. Corrosion will cause the wiring to become constricted much in the same way that a kinked garden hose is constricted from delivering water. Corrosion causes resistance, and resistance causes electrical devices to function improperly or not at all. Good practice is to keep the battery terminals consistently clean and tight fitting, but it is equally important to locate and clean the ground lugs and critical harness connectors to prevent corrosion from building and creating an electrical problem.

Let's say the starter or other electrical load is not working properly, and you're not sure if there is a voltage drop problem on a circuit or across a terminal. A quick and easy test for this involves the use of our handy DVOM. Place the meter on the DC volts scale, then attach one meter lead to one end of the positive lead to the electrical device at the source and the other meter lead to the other end of the positive lead where it ends at the device. (You're creating a parallel path for the positive current to travel through the meter on the way to the device. Ideally, electrical current shouldn't seek the alternate path though the meter, but when it does…it indicates that there is resistance on that electrical circuit). Energize the device (such as the starter) with the meter connected as described. If anything greater than about .2volt DC shows on the meter, there is voltage drop on the circuit that needs to be fixed. Best of all, this quick test works great to isolate resistance problems in almost all wiring, including ground circuits. The best way to reduce the possibility of corrosion and the related problems is storing the vehicle in a dry environment and placing desiccant bags in the interior and trunk to absorb any residual moisture.

In summary, proper put away involves preserving the integrity of the electrical system through maintaining a correct battery state-of-charge, eliminating any parasitic electrical draws and keeping the prospect of corrosion and moisture problems out of the picture. Prevention is well worth the time well invested!