16.  HOW CAN I REVIVE A SULFATED BATTERY?

Starting and other lead-acid batteries are perishable. During the 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 under charged, or the electrolyte level is below the top of the plates, some of the soft lead sulfate re-crystallizes into hard lead sulfate. It cannot be reconverted during subsequent recharging. This creation of hard crystals is commonly called " lead sulfation". It accounts for over 80% of the deep cycle lead-acid battery failures. The longer sulfation occurs, the larger and harder the lead sulfate 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.

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 switch is turned off. The load is from the continuous operation of electrical appliances, such as, an emmissions computer, a 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 other problem, the natural self-discharge of battery. Thus, sulfation can be a huge problem for lead-acid batteries while sitting on a dealer's shelf, in a basement, or in a parked vehicle, especially in hot temperatures.

16.1. 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. 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 13.2 VDC and 13.6 VDC, measured at 70° F (21.1° C) with an accurate (.5% or better) digital voltmeter. Charging can best be accomplished with a microprocessor controlled three stage or four stage charger, such as a Battery Tender (Deltran), Truecharge (Statpower), BatteryMinder, Schumacher, etc., or by voltage regulated float charger set at the correct voltage, such as a ChargeTek, etc. By contrast, a cheap, unregulated "trickle" charger or manual two stage 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 12.63 VDC and at 80% State-of-Charge, it 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, 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 than 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.

16.2. How do I recover sulfated batteries?

Here are three methods to try to recover sulfated batteries:

16.2.1. Light Sulfation

Apply a constant current from one to two amps for 48 to 120 hours at 14.4 VDC, 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 sulfate crystals.  If the battery gets above 110° F (43.3° C) then stop charging and allow the battery to cool down before continuing.

16.2.2. Heavy Sulfation

Replace the electrolyte with DISTILLED water, let stand for one hour, apply a constant current at four amps at 13.8 VDC 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 sulfate 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 sulfate crystals are more soluble in water than in electrolyte. As these crystals are dissolved, the sulfate is converted back into sulfuric acid and the specific gravity rises.  This procedure will only work with some batteries.

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