TEMPERATURE IN DEGREES C (F)
[Source: Concorde]
Last Updated on January 16, 2005
13.1. How Do I Prevent Permanent Sulfation?
13.2. So How Do I Store My Battery?
If not used weekly, people kill more deep cycle and power sport batteries with bad charging and maintenance practices, than die of old age!
All lead-acid batteries are perishable. During the normal discharge process, soft lead sulfate crystals are formed in the pores and on the surfaces of the positive and negative plates inside a lead-acid battery. When a battery is left in a discharged condition, is continually undercharged, excessive temperatures or the electrolyte level is below the top of the plates, some of the soft lead sulfate re-crystallize into hard lead sulfate. It cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called permanent "sulfation". It is the leading cause and accounts for approximately 85% of the premature failures of lead-acid batteries not used weekly. The longer sulfation occurs, the larger and harder the lead sulfate crystals become. The positive plates will turn a light brown and the negative plates will be dull, off white. These permanent crystals lessen a battery's capacity and ability to be recharged. Deep cycle batteries that are typically used for short periods and then are stored for long periods where they slowly self discharge. A car or motorcycle starting battery that is normally used several times a month, so permanent sulfation rarely becomes a problem unless it is unused or stored for long periods.
While a battery is in storage or not being used, the discharge is a consequence of parasitic load or natural self discharge. Parasitic load is the constant electrical load present on a battery while it is installed in a vehicle even when the ignition key is turned off. The load is from the continuous operation of electrical appliances, such as an emissions computer, clock, security system, maintenance of radio station presets, etc. While disconnecting the negative battery cable will eliminate the parasitic load, it has no affect on the natural self discharge of battery. Thus, permanent sulfation can be a huge problem for lead-acid batteries while sitting for long periods on a dealer's shelf, in a basement, cellar, barn or garage, or in a parked vehicle, especially in hot temperatures.
13.1. How Do I Prevent Permanent Sulfation?
The best way to prevent sulfation is to keep a lead-acid battery fully charged because lead sulfate is not formed. This can be accomplished three ways. Based on the battery type you are using, the best solution is to use a charger in a well ventilated area that is capable of delivering a continuous, temperature compensated "float" charge at the battery manufacturer's recommended float or maintenance voltage for a fully charged battery. For 12-volt batteries, depending on the battery type, usually have fixed float voltages between 13.1 VDC and 13.6 VDC, measured at 80° F (26.7° C) with an accurate (.5% or better) digital voltmeter. (For a six-volt battery, measured voltages are one half of those for a 12-volt battery.) This can best be accomplished by continuously charging using a three stage for VRLA (AGM or Gel Cell) batteries or four stage for wet (flooded) batteries, "smart" microprocessor controlled charger. If you already have a two stage charger, then use a voltage-regulated "float" charger or battery "maintainer", set at the correct float voltage to "float" or maintain a fully charged battery. If you need Web addresses or telephone numbers of the charger manufacturers, please see the Chargers and Float Chargers and Battery Maintainers sections of Battery Information Links List. A cheap, unregulated "trickle" or a manual two stage charger can overcharge a battery and destroy it by drying out the electrolyte.
A second and less desirable method is to periodically recharge the battery when the State-of-Charge drops to 80% or below. Maintaining a high State-of-Charge tends to prevent irreversible permanent sulfation. The frequency of recharging depends on the parasitic load, temperature, battery's condition, and battery type. Temperature matters! Lower temperatures slow down electro chemical reactions and higher temperatures will significantly increase them. A battery stored at 95° F (35° C) will self discharge twice as fast than one stored at 75° F (23.9° C). Standard (Sb/Sb) batteries have a very high self-discharge rate; whereas, AGM batteries have a very slow rate.
There are trade-offs between the economics of continuous "float" charging, where self discharge and resulting sulfation does not occur, and periodic charging with the increased potential for a shorter battery life due to permanent sulfation. If you decide to periodically recharging the batteries while in storage, increased recharging frequency, disconnecting any parasitic load, or storing them in colder temperatures will impede the self discharge and reduce the possibility for permanent sulfation, but will also reduce the total number of life cycles.
A third technique is to use a solar panel designed to "float" charge batteries. This is a popular solution when AC power is unavailable for charging. The size of panel requires will depend on the amount of available sunlight and battery capacity. Normally a 5 watt or larger panel is required for a car battery. A charge controller (voltage regulator) is required when the peak current output of the panel exceeds 1.5% of the capacity of the battery.
13.2. So How Do I Store My Battery?
Batteries naturally self discharge 1% to 60% per month (depending on the battery type and temperature) while not in use and sulfation will begin occurring when the State-of-Charge (SoC) drops below 100%. Please see Section 16 for more information on sulfation. Cold will slow the process down and heat will increase it up. Storing batteries under 250 AH on concrete floors will not cause them to naturally self discharge faster. Please see Section 14.1 for more information on this myth. Below are six simple steps while your batteries are not in use to protect them from permanent sulfation and premature failure.
13.2.1. Physically inspect for leakage or damaged cases, remove any corrosion, clean and dry the tops of the batteries to remove possible discharge paths from dried battery electrolyte, and clean the terminals. If the battery is in a vehicle, remove the negative connection from the battery to eliminate the additional parasitic (key off) discharge.
13.2.2. If the battery has filler caps, check the electrolyte (battery acid) level in each cell. If required, add only distilled, deionized or demineralized water to the recommended level, but do not overfill.
13.2.3. Fully charge and equalize wet (flooded) batteries, if required, using the procedures in Section 9 and recheck the electrolyte levels when th battery cools.
13.2.4. Store in a cold dry place, but not so that it will freeze, and where it can be easily recharged. The freezing point of a battery is determined by the SoC and the higher it is, the lower the freezing temperature. Please see the State-of-Charge Table in Section 4. Based on the battery type you are using, connect a "smart", microprocessor based three stage or four stage charger or a voltage regulated float charger to continuously "float" charge your battery. Do not use a cheap, unregulated "trickle" charger or a manual two stage charger which was not designed for "float" charging or you will overcharge your battery. A less desirable alternative to float charging would be to periodically test the State-of-Charge using the procedure in Section 4. When it is 80% or below, recharge using the procedures in Section 9. The frequency of testing and recharging will depend on the ambient storage temperature.
FLOAT CHARGING VOLTAGE
TEMPERATURE IN DEGREES C (F)
[Source: Concorde]
13.2.5. Periodically test the State-of-Charge (SoC) and ensure that the electrolyte is at the proper levels.
13.2.6. When you remove the batteries from storage, charge and equalize, if required, using the battery manufacturer's recommended charging procedures or, if not available, the one in Section 9.