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Discharging at High and Low Temperatures

Like humans, batteries function best at room temperature. Warming a dying battery in a mobile phone or flashlight in our jeans might provide additional run time due to improved electrochemical reaction. This is likely also the reason why manufacturers prefer to specify batteries at a toasty 27°C (80°F). Operating a battery at elevated temperatures improves performance but prolonged exposure will shorten life.

The dry solid polymer battery requires a temperature of 60–100°C (140–212°F) to promote ion flow and become conductive. This type of battery has found a niche market for stationary power applications in hot climates where heat serves as a catalyst rather than a disadvantage. Built-in heating elements keep the battery operational at all times. High battery cost and safety concerns have limited the application of this system. The more common lithium-polymer uses gelled electrolyte to enhance conductivity.

All batteries achieve optimum service life if used at 20°C (68°F) or slightly below. If, for example, a battery operates at 30°C (86°F) instead of a more moderate lower room temperature, the cycle life is reduced by 20 percent. At 40°C (104°F), the loss jumps to a whopping 40 percent, and if charged and discharged at 45°C (113°F), the cycle life is only half of what can be expected if used at 20°C (68°F).

The performance of all batteries drops drastically at low temperatures; however, the elevated internal resistance will cause some warming effect because of efficiency loss during use. At –20°C (–4°F) most batteries are at about 50 percent performance level. Although NiCd can go down to –40°C (–40°F), the permissible discharge is only 0.2C (5-hour rate). Specialty Li-ion can operate to a temperature of –40°C but only at a reduced discharge rate; charging at this temperature is out of the question. With lead acid there is the danger of the electrolyte freezing, which can crack the enclosure. Lead acid freezes quicker with a low charge when the specific gravity is more like water than when fully charged.

How to Verify Sufficient Battery Capacity

Know how to maintain a battery fleet and eliminate the risk of unexpected downtime.

A battery performs well when new but the capacity soon begins to fade with use and time. To assure reliable service during the life span of the battery, design engineers oversize the pack to include some spare capacity. This is similar to carrying extra fuel in an airplane to enable a waiting pattern or attempt a second landing approach when so required.

New batteries operate (should operate) at a capacity of 100 percent; replacement occurs when the packs fade to about 80 percent. All batteries must include a secure level of spare capacity to cover worst-case scenarios.

In addition to normal capacity fade, cold temperature lowers the capacity, especially Li-ion. The capacity loss of a Li-ion Energy Cell is about 17 percent at 0°C (32°F), 34 percent at –10°C (14°F) and 47 percent at –20°C (–4°F). Power Cells perform better at cold temperature with lower cold-related capacity losses than Energy Cells.

Lack of spare capacity is a common cause of system failures. This commonly happens during heavier than normal traffic or in an emergency. During routine operations, marginal batteries can hide comfortably among their peers, but they will fail when put to the test. A battery maintenance program as part of quality control assures that all batteries in the fleet are within the required performance range.

If packs with fringe capacity levels come back from a full-day shift with less than 10 percent of spare capacity, raise the pass/fail target capacity from 80 to 85 percent to gain five extra points. If, on the other hand, these old-timers come back with 30 percent before charging, keep them longer by lowering the target capacity to, say, 70 percent. Knowing the energy needs for each application during a typical shift increases battery transparency. This improves reliability and creates a sweet spot between risk management and economics.


How long do batteries last in wireless alarm sensors?


The average Lithium battery in a wireless alarm sensor will probably last somewhere between 3 and 5 years. Battery life in wireless sensors can vary greatly. The type and model of wireless sensor is the primary contributing factor. Refer to the manual for your device to determine what the manufacturer states the average battery life will be. Another factor could be the type of battery used, such as alkaline vs.lithium. Usually, lithium batteries will last longer, and most modern alarm sensors now use them. Each wireless sensor will have specifications with regard to the batteries that can be used. DO NOT USE BATTERIES NOT APPROVED BY THE MANUFACTURER. Frequency of use is also a contributing factor to the length of battery life, or lack thereof. For example, a door that is opened and closed hundreds of times a day will wear down its battery on the door contact much more quickly than the same sensor on a window that is rarely opened.
 

Click box to see a list of batteries and the devices associated.