People kill more deep cycle batteries with poor charging practices, than die of old age!

Deep cycle and other lead-acid batteries are perishable. During the discharge process, soft lead sulphate 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 under charged, or the electrolyte level is below the top of the plates, some of the soft lead sulphate re-crystallizes into hard lead sulphate. It cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called " lead sulphation". It accounts for over 80% of deep cycle lead-acid battery failures. The longer sulphation occurs, the larger and harder the lead sulphate crystals become. The positive plates will be light brown and the negative plates will be dull, off white. These crystals lessen a battery's capacity and ability to be recharged. This is because deep cycle batteries are typically used for short periods and then are stored for the rest of the year while they are slowly discharging. In contrast, a starting battery is normally used several times a month, so sulphation rarely becomes a problem.

Sulphation 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 power is turned off. The load is from the continuous operation of appliances, such as a clock, security system, maintenance of radio station presets, etc. While disconnecting the negative battery cable will eliminate the parasitic load, it has no effect on the other problem, the natural self-discharge of battery. Thus, sulphation can be a huge problem for lead-acid batteries which are not being used while in storage or are sitting on a dealer's shelf, in a basement or in a parked vehicle, especially in hot temperatures.

  1. How do I prevent sulphation?
  2. The best way to prevent sulphation is to keep a lead-acid battery fully charged because lead sulphate is not formed. This can be accomplished in three ways. The best solution is to use a charger that is capable of delivering a continuous "float" charge at the battery manufacturer's recommended float or maintenance voltage for a fully charged battery. 12-volt batteries, depending on the battery type, usually have fixed float voltages between 13.2V DC and 13.6V DC, measured with an accurate (.5% or better) digital voltmeter at 70°F (21.1°C). Charging can best be accomplished with a microprocessor controlled three stage or four stage charger or by a voltage regulated float charger set at the correct voltage. By contrast, a cheap unregulated "trickle" charger can over charge a battery and destroy it.

    A second and less desirable method is to periodically recharge the battery when the State-of-Charge drops to 80% or below. At 70°F (21.1°C) a battery with 100% State-of-Charge measures approximately 1.261 Specific Gravity or 12.63V DC and at 80% State-of-Charge it measures 1.229 Specific Gravity or 12.47V DC. Maintaining a high State-of-Charge tends to prevent irreversible sulphation. The recharge frequency is dependent on the parasitic load, temperature, the battery's condition, and plate formulation (battery type). Temperature matters! Lower temperatures slow down electro chemical reactions and higher temperatures speed them up. A battery stored at 95°F (35°C) will self-discharge twice as fast as one stored at 75°F (23.9°C).

    A third technique is to use a regulated solar panel or wind generator designed to float charge the battery. This is a popular solution when AC power is unavailable for charging.

  3. How do I recover sulphated batteries?
  4. Here are three methods to try to recover sulphated batteries:

    1. Light Sulphation
    2. Apply a constant current from one to two amps for 48 to 120 hours at 14.4V DC, depending on the electrolyte temperature and capacity of the battery. Cycle (discharge to 50% and recharge) the battery a couple of times and test its capacity. You might have to increase the voltage in order to break down the hard lead sulphate crystals. If the battery gets above 110°F (43.3°C) then stop charging and allow the battery to cool down before continuing.

    3. Heavy Sulphation
    4. Replace the electrolyte with DISTILLED water, let stand for one hour, apply a constant current at four amps at 13.8V DC until there is no additional rise in specific gravity, remove the electrolyte, wash the sediment out, replace with fresh electrolyte, and recharge. If the specific gravity exceeds 1.300, then remove the old electrolyte, wash the sediment out, and start over with distilled water. You might have to increase the voltage in order to break down the hard lead sulphate crystals. If the battery gets above 110°F (43.3°C) then stop charging and allow the battery to cool down before continuing. Cycle (discharge to 50% and recharge) the battery a couple of times and test capacity. The sulphate crystals are more soluble in water than in electrolyte. As these crystals are dissolved, the sulphate is converted back into sulfuric acid and the specific gravity rises. This procedure will only work with some batteries.