MadSci Network: Engineering

Re: How does temperature affect batteries??

Date: Tue Jul 20 17:20:44 1999
Posted By: Michael L. Roginsky, Staff, Avionics, Honeywell Defense Avionics
Area of science: Engineering
ID: 926829295.Eg

Hello Bridget:

Thanks for your question. I assume you are referring to the common lead-acid battery. Lead-acid batteries reach peak efficiency at 90 degrees F (32 C) As ambient temperature drops, ampere output and recharging efficiency decline, dropping to 40 percent of rated output at 0 degree F (-18 degree C). Cold Cranking Ampere (CCA) rating is the best yardstick by which to measure a battery's capacity. It indicated the discharge rate (measured in amperes) a fully charged battery will maintain at 0 degrees F (-17.8 degree C) without terminal voltage dropping below 1.2 volts per cell. The last major concern regarding battery applications is the environment in which it is used, specifically the temperatures at which the battery is required to operate. Batteries and people like approximately the same temperature range. If the temperature gets too warm, the chemical reactions within the battery are accelerated and its life may be shortened. If the battery gets too cold, the chemical reactions are slowed down which reduces the battery output. In other words, like all chemical processes, lead acid battery performance is temperature dependent. The available capacity and maximum current both fall at low temperature, and increase, although to a lesser degree, at raised temperatures. The risk of freezing is also real for a fully discharged battery at temperatures not so far below zero. The chemistry slows down as temperature falls; this applies equally well to charging as discharge. To optimize performance over a wide temperature range, it is important to recognize the temperature related factors in both the charging arrangement any low voltage disconnection scheme that may be employed. The charging voltage needs to be raised as temperature falls to ensure that the battery continues to accept charge, although it may be necessary to provide an upper limit on this raised voltage to ensure that any load equipment that remains connected during charging is not operated outside of its specified range.

Heat stagnation can cause thermal runaway. Thermal runaway is a critical condition arising during constant voltage charging in which the current and the temperature of a battery produce a cumulative mutually reinforcing effect that further increases them and can lead to the destruction of the battery. An aging factor in lead acid batteries is the corrosion of the current collector grid. The choice alloys for battery grids are lead-calcium-tin and lead-tin alloys with the calcium level ranging from 0.03 to 0.09 % and the tin level from 0.3 to 2.0 %. More exotic alloys containing lead-antimony-cadmium and lead-strontium-tin are also in use or have been proposed. The grids of the positive plate of a lead acid battery are subject to a corrosion process in which lead (Pb) is transformed into lead dioxide (PbO2). The corrosion rate increases with temperature (doubling approximately every 10C), float voltage and acid concentration. The corrosion attack may be an area type attack or a grain boundary attack or a combination of both. The corrosion product, lead dioxide, requires a 37% higher volume then the lead source material. This volume expansion induces mechanical forces in the grid that becomes deformed and stretched. This deformation is called growth and reduces the contact of the current collector (grid) with the active material. A capacity reduction occurs. At a growth level of 4-7%, grid fractures and capacity losses of the battery occur. In extreme case internal shorting and cell case rupture may ensue. The transformation of lead into lead dioxide consumes also the water of the electrolyte (1g Pb= 0.17g water) which further impinges on the performance of the battery.

Lead-acid batteries do not respond well to deep discharges and store progressively smaller amounts of energy when recharged. It is very important to keep the level of liquid in each cell replenished, especially in hot weather. BE SURE TO WEAR EYE PROTECTION when doing so. The sulfuric acid used as the electrolyte is extremely hazardous. Also beware that hydrogen is a byproduct of the charging process, and it is FLAMABLE! When jump starting a car, always connect both terminals to the dead battery first to prevent explosion hazard.

I found an internet link you may wish to explore:

I hope this info is helpful. MAD.SCI MICRO

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