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Lead Acid Battery Basics

1. A lead acid battery is made up of plates, lead, and lead oxide and contains a 36% sulfuric acid and 64% water solution. This solution is called the electrolyte which causes a chemical reaction that will produce electrons. Testing a battery with the hydrometer will measure the amount of sulfuric acid left in the electrolyte solution.

2. Any lead acid battery can be a BOMB. Please, be safe when working with or around lead acid batteries. The hydrogen gas that batteries make when being charged is very explosive. When doing any type of electrical work on vehicles it is a good idea to disconnect the ground cable and remove all your jewelry. Just remember you are messing with corrosive acid and explosive gases.

3. Basically there are two types of lead acid batteries, one for starting (cranking), and then a deep cycle(marine). The starting battery is designed to deliver a quick burst of power. A deep cycle battery has less instant power but has greater long term power delivery. Deep cycle batteries have a thicker plate and can survive a greater number of charge and discharge cycles.

4. There are three versions of lead acid batteries, Wet Cell, Gel Cell, and the new Absorbed Glass Mat (A G M). The wet cell comes in 2 styles; serviceable, and then there is maintenance free. Both are filled with electrolyte. The Gel-Cell and the AGM batteries are specialty batteries that typically cost twice as much as the premium wet cell. They store well and do not tend to sulfate as easily as a wet cell. There is no chance of a hydrogen gas explosion when using these batteries. Gel-Cell batteries are still being sold but the AGM batteries are becoming more popular. AGM batteries will give almost double the life span and many more deep cycles than a wet cell battery.

5. CCA, CA, RC and AH are the standards that most battery companies will use to rate the output and the capacity of a battery.

Cold cranking amps (CCA) is a measurement of the number of amps a battery can deliver at 0 degrees F for 30 seconds and not go below 7.2 volts. A high CCA battery rating is good for cold weather.

CA is cranking amps measured at 32 degrees F.

Reserve Capacity (RC) is an important rating. This is the number of minutes a fully charged battery at 80 degrees F will discharge 25 amps until the battery drops below 10.5 VDC.

Amp hours (AH) is a rating usually found on a deep cycle battery. If a battery is rated for 100 amp hours it should deliver 5 amps for twenty hours or twenty amps for 5 hours,

If you have a maintenance free wet cell then the only way to test is to use a voltmeter and a load test. Most of the maintenance free batteries have a built in hydrometer, this tells you the condition of one cell of the six. You may get a good reading from the one cell but have a problem with some other cells.

6. Battery life and performance - The average battery life has become shorter as energy requirements have increased. Only 30% of the batteries sold today last for 48 months. 80% of all battery failure is related to a sulfation build up. This build up occurs when the sulfur molecules in the electrolyte become deeply discharged that they begin to coat the battery's lead plates. The plates become so coated that the battery will die.

7. The battery should be cleaned using a baking soda and water. Cable connections need to be tight and tight. Many battery problems are caused by a dirt or a loose connection. A good battery needs to have the fluid level checked. Distilled water is best. Do not over fill battery cells especially in the warmer weather. The natural fluid expansion in hot weather will push electrolytes from the battery. To prevent corrosion of cables on the top post you can apply a small bead of silicon at the base of the post and then place a felt battery washer over the base. Coat the washer with high temp grease or petroleum jelly, then place the cable on the post and tighten it down. Coat the exposed cable end with grease. The gases from the battery condensing on the metal parts will cause corrosion.

8. The water level of the battery must be above the plates. Plates exposed to air will sulfate quickly. Proper water level is easily detected by removing the cover and looking at cells.

9. A cell that is low on water will look flat. Like the cell below on the right.


When the water reaches the proper level it will bend when contacting the bottom edges of the vent well. The cell on the left has the proper level of water.

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