Pulled this from a newsgroup. 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 or is continually undercharged, some of the soft lead sulfate is re-crystallizes into hard lead sulfate, which cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called sulfation and is the most common cause of failure of lead-acid batteries while in storage. The longer sulfation occurs, the larger and harder the lead sulfate crystals become. These crystals lessen a battery s capacity and ability to be recharged. People kill more deep cycle batteries (due to sulfation) with poor charging practices, than die of old age. This is because a deep cycle battery is typically used for short periods and then is stored the rest of the year why they are slowly discharging. In contrast, a car or motorcycle battery is normally used several times a month, so sulfation rarely becomes a problem. Sulfation is a result of lead-acid battery discharge while in storage, which is a consequence of parasitic load and 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 appliances, such as an emissions computer, the clock, a security system, and the maintenance of radio station presets in a radio.] While disconnecting the negative battery cable will eliminate the parasitic load, it has no affect on the other problem, the natural self-discharge of battery. Thus, sulfation can be a huge problem for lead-acid batteries not being used while in storage or sitting on a dealer s shelf, in a basement, or in a parked vehicle. How do I prevent 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. (1) The best solution is to use a charger that is capable of delivering a continuous float or trickle charge at the battery manufacturer s recommended float or maintenance voltage for a fully charged battery. 12-volt batteries and depending on the battery type, usually have fixed float voltages between 13.2 VDC and 13.6 VDC, measured at 70 degrees F (21.1 degrees C) with an accurate (.5% or better) digital voltmeter. For a six-volt battery, measured voltages are one half of a 12-volt battery. Charging can best be accomplished with a microprocessor controlled three- or four-stage charger, such as a, Battery Tender (Deltran), Truecharge (Statpower), BatteryMinder, Schumacher, ChargeTek, etc., or by voltage-regulated (or constant voltage) charger set at the correct float voltage. By contrast, a cheap, unregulated trickle charger can overcharge a battery and destroy it. (2) A second method is to periodically recharge the battery when the State-of-Charge drops from 100% to 80%. At 70 degrees F (21.1 degrees C), a battery with 100% State-of-Charge measures approximately 1.261 Specific Gravity or 12.63 VDC and 80% State-of-Charge measures 1.229 Specific Gravity or 12.47 VDC. Maintaining a high State-of-Charge tends to prevent irreversible sulfation. The recharge frequency is dependent on the parasitic load, temperature, a battery s condition, and plate formulation (battery type). Temperature matters! Lower temperatures slow down electrochemical reactions and higher temperatures speed them up. A battery stored at 95 degrees F (35 degrees C) will self-discharge twice as fast than one stored at 75 degrees F (23.9 degrees C). (3) A third technique is to use a solar panel or wind generator to float charge the battery. This is a popular solution when AC power is unavailable for charging. So how do I store my battery? There are three simple steps. First, if the battery has filler caps, check the electrolyte (battery acid) level in each cell. If required, add only distilled water to the recommended level, but do not overfill; clean the top of the battery and posts; and fully charge the battery. Second, store the battery in a cool (above freezing), dry place where it can be easily recharged. Finally and most importantly, prevent sulfation by keeping the battery charged above the 80% State-of-Charge level!