Explore the limitations when operating a battery at adverse temperatures and learn how to minimize the effects.
Like humans, batteries function best at room temperature, and any deviation from the comfort zone changes performance and/or longevity. While operating a battery at elevated temperatures momentarily improves performance by lowering the internal resistance and speeding up the chemical metabolism, such a condition shortens service life. Some manufacturers of lead acid batteries make use of improved performance at warmer temperatures and specify the batteries at a toasty 27°C (80°F).
Cold temperature increases the internal resistance and lowers the capacity. Batteries that would provide 100 percent capacity at 27°C (80°F) will typically deliver only 50 percent at –18°C (0°F). The capacity decrease is momentary and the level of decline is related to the battery chemistry.
Li-ion also performs better when warm. Heat lowers the internal resistance but this stresses the battery. Warming a dying flashlight or cellular phone battery in your jeans might provide additional runtime due to better energy delivery. As all drivers in cold countries know, a warm battery cranks the car engine easier than a cold one.
The dry solid-polymer battery requires a temperature of 60–100°C (140– 212°F) to promote ion flow and get 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 moist 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 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). (See also BU-808: How to Prolong Lithium-based Batteries.)
The performance of all battery chemistries drops drastically at low temperatures. At –20°C (–4°F) most nickel-, lead- and lithium-based batteries stop functioning. 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; charging at this temperature is out of question. With lead acid there is the danger of the electrolyte freezing, which can crack the enclosure. Lead acid freezes more easily with a low charge when the specific gravity of the electrolyte is more like water than when fully charged.
Cell matching by using cells of similar capacity plays an important role when discharging at low temperature under heavy load. Since the cells in a battery pack can never be perfectly matched, a negative voltage potential can occur across a weaker cell on a multi-cell pack if the discharge is allowed to continue beyond a safe cut-off point. Known as cell reversal, the weak cell will get damaged to the point of developing a permanent electrical short. The larger the cell-count, the greater the likelihood of cell-reversal is under load. Over-discharge at a heavy load at a low temperature is also a large contributor to battery failure of cordless power tools, especially nickel-based packs. (See BU-803: Can Batteries be Restored? Go to Cell Mismatch, Balancing.)
Users of electric vehicles must understand that the driving distance between charges is calculated under normal temperature; frigid cold temperatures will reduce the available mileage. Using battery electricity to heat the cabin is not the only reason for reduced driving distance; the battery does not perform well when cold but it will recuperate when warm.
Last updated 2015-03-30
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