Storing Electricity for the Off-Season
Battery & Electrical ConsiderationsSit back and consider for a moment that we refer to automotive batteries as "storage" batteries, an appropriate reference since we count on the battery to hold enough potential energy to ensure consistent, reliable starting even after prolonged periods of inactivity. But storage can also refer to the long-term "put away" that many collector, hobby, and special interest vehicles experience during the winter months -- and the demands that this hibernation will inevitably place upon the battery and associated electrical components. A basic understanding of electrical theory and practical application with emphasis on the battery can mean the difference between experiencing a frustrating diagnostic issue and a gratifying quick startup come springtime.
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
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.
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
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!