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The site was purchased in April 1957, and construction began in February 1958. On July 31, 1958, Smith received a cable from Theodore Emmett, executive vice president of Ford of Canada, asking him to come to the U.S. The Glass, Elliot, and Gutta-Percha Companies were united to form the well-known Telegraph Construction and Maintenance Company, which undertook to manufacture and lay the new cable. Electric companies have used this technology for years to monitor the performance of power grids. The term shelf life is used to describe how long a battery will retain its performance between manufacture and use. A deep-cycle battery can supply power for a day or two at that level. One other thing to note is that if you plan to operate sensitive equipment like TVs and computers from an emergency power supply, you will want to have in place excellent surge protection equipment and, in the case of a computer, an uninterruptible power supply (UPS). The rated capacity of a battery is usually expressed as the product of 20 hours multiplied by the current that a new battery can consistently supply for 20 hours at 20 °C (68 °F), while remaining above a specified terminal voltage per cell.

Typically, maximum capacity is found at a low C-rate, and charging or discharging at a higher C-rate reduces the usable life and capacity of a battery. The C-rate is a measure of the rate at which a battery is being charged or discharged. Old rechargeable batteries self-discharge more rapidly than disposable alkaline batteries, especially nickel-based batteries; a freshly charged nickel cadmium (NiCd) battery loses 10% of its charge in the first 24 hours, and thereafter discharges at a rate of about 10% a month. However, newer low self-discharge nickel-metal hydride (NiMH) batteries and modern lithium designs display a lower self-discharge rate (but still higher than for primary batteries). Sound detectors remained on guard in 1944 (even with radar in use), with military personnel still listening for enemy airplanes. This is known as the "self-discharge" rate, and is due to non-current-producing "side" chemical reactions that occur within the cell even when no load is applied. The active material on the battery plates changes chemical composition on each charge and discharge cycle; active material may be lost due to physical changes of volume, further limiting the number of times the battery can be recharged. Because of internal resistance loss and the chemical processes inside the cells, a battery rarely delivers nameplate rated capacity in only one hour.

It is defined as the current through the battery divided by the theoretical current draw under which the battery would deliver its nominal rated capacity in one hour. The fraction of the stored charge that a battery can deliver depends on multiple factors, including battery chemistry, the rate at which the charge is delivered (current), the required terminal voltage, the storage period, ambient temperature and other factors. As such, in cold climates, some car owners install battery warmers, which are small electric heating pads that keep the car battery warm. The charger does not create enough amperage immediately to satisfy the needs of the starter motor, and will be unable to jump-start the car. After enough recharges, in essence all capacity is lost and the battery stops producing power. For rechargeables, it can mean either the length of time a device can run on a fully charged battery or the number of charge/discharge cycles possible before the cells fail to operate satisfactorily. Standards for rechargeable batteries generally rate the capacity and charge cycles over a 4-hour (0.25C), 8 hour (0.125C) or longer discharge time. NiCd batteries tend to be rated for 1,000 cycles before their internal resistance permanently increases beyond usable values.

Disposable batteries typically lose 8-20% of their original charge per year when stored at room temperature (20-30 °C). By carefully routing the home's plumbing, water can be heated by the sun and, as the water is pumped through the house, the heat can be dissipated to help control the house's temperature. A 4.4 MWh battery system that can deliver 11 MW for 25 minutes stabilizes the output of the Auwahi wind farm in Hawaii. Battery life (and its synonym battery lifetime) has two meanings for rechargeable batteries but only one for non-chargeables. Such storage can extend the life of alkaline batteries by about 5%; rechargeable batteries can hold their charge much longer, depending upon type. The rate of side reactions is reduced for batteries stored at lower temperatures, although some can be damaged by freezing and storing in a fridge will not meaningfully prolong shelf life and risks damaging condensation.

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