Store batteries at a low temperature if possible - 5deg C is ideal. Although capacity goes up with temperature, the life of a battery goes down.
The self discharge rate goes down with temperature. At room temperature, recharge stored batteries every 6 months; storage at 5C lets you wait 18 months before recharging.
Rechargeable batteries will not stay fully-charged sitting on the shelf. They begin to lose their charge after a few days, and will lose about 5% of their charge every day thereafter.
Lead-acid batteries should be recharged after every use, even if only a small amount of their charge has been used.
Batteries are sensitive to extreme temperatures, and won't perform well below 0 degrees Celsius (32 F) or above 40 degrees Celsius (100 F).
The rate of chemical reactions is strongly temperature dependent, Thus, batteries (cells) will self discharge over time even it they are not being used.
The output of most batteries are very dependent upon their temperature. The reactions producing the output fail rapidly as the temperature is lowered.
The rate at which a battery is discharged and its operating temperature have a profound effect on its capacity and life.
The depth of discharge also affects the life of a battery.
Colder operating temperatures will yield a little extra life, but also lower the capacity of lead- acid cells. High temperatures yield higher capacity (see Figure 11) but have a detrimental effect on life.
Cycle life of the battery is dependent on the depth of discharge in each cycle. The deeper the discharge is, the shorter the cycle life (smaller number of cycles), providing the same discharge current.
Trickle Life - The service life of a battery is in the trickle use. Usually, the trickle life is the time expressed in years before the dischargeable time of the battery decreases to a half of the initial value.
Trickle life of the battery is largely dependent on the temperature condition of the equipment in which the battery is used, and also related to the type of the battery, charge voltage and discharge current.
There is much confusion about "battery voltage" because a battery has more than one voltage and often the literature is lax in defining which voltage is being discussed at the time. Also, measurements of a batteries voltage, particularly float voltage, require time (that is often not allotted) for the battery to stabilize.
Float Voltage - Battery voltage at zero current (with battery disconnected). You must wait about 20 minutes for the battery to stabilize at this voltage.
Nominal Voltage - The Voltage that a battery is referred to. i.e. a 12 Volt battery is made of 6 cells and has a Float voltage of about 12V.
Charge Voltage - The voltage a battery goes to while being charged.
Discharge Voltage - The voltage of a batter while discharging. Again, this voltage is determined by the charge state and the current flowing.
Energy efficiency is calculated on the amount of power used from the battery while discharging divided by the amount of power delivered to the batter while charging, multiplied by 100 to yield percent. Pout x 100 /Pin .
A lead-acid battery has an efficiency of only 75-85%.
The energy lost appears as heat and warms the battery.
Keeping the charge and discharge rate of a battery low, helps keep a battery cool and improves the battery life. The above losses don't include losses in the charging circuit which can run any where from 60 to 80% - thus the overall- total efficiency is the product of these numbers and ends up being 45 to 68%.
(To further this example and to show why physics and not some corporate conspiracy is the reason we don't have electric cars - suppose the controls and motors on a car were 85% - the over all efficiency is now only 38 - 58%. You can see that an electric car would use about twice the energy of a conventional car - not to mention the great cost of the regular replacement of batteries. This is why batteries are best used where only intermittent, or very low power use is required.)
Battery capacity refers to the total amount of energy stored within a battery. Rated capacity is in Ampere-hours (AH), which is the product of the current times the number of hours to total discharge. The capacity is normally compared with a time of 20 hours and a temperature of 68F (20C). There are five factors that dictate the capacity of a given battery:
Size - The volume and plate area of a battery increases with capacity.
Temperature - As a battery gets colder, its capacity decreases.
Cut off voltage - To prevent damage, the cut-off voltage should be limited to 1.67V or 10V for a 12 Volt battery.
Discharge rate - This is the rate of discharge, measured in amperes. As the rate goes up, the capacity goes down.
History - Deep discharging, excessive cycling, age, over charging, under charging, all reduce capacity.
However, YOU don't need to become a battery expert. ELESCO has the experts who are available to take care of your batteries for you and service your specific equipment.
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Saturday, May 27, 2006