The Meaning of Deep Cycle
In battery terms "cycle" means a discharge and recharge. "Deep Cycle" refers to a discharge that approaches the battery's rated capacity followed by a full recharge. Normally a lead acid battery's nominal charge is 2 Volts per cell. When fully discharged the voltage drops to 1.75 Volts per cell. All batteries will "deep cycle" a few times but only "Deep Cycle" batteries will withstand hundreds of cycles and still be ready for more.
Deep Cycle Rating
20 hour capacity is the most universal rating for Deep Cycle storage batteries and is expressed in Ampere Hours (AH). It indicates the total capacity a battery can supply in a 20 hour period using a fixed current draw to reach a discharge point of 1.75 Volts per cell.
Sizing Considerations
Lead acid batteries are composed of 2 Volt cells. Deep Cycle batteries operate in sets to achieve a desired voltage and/or amp hour capacity. Batteries can be connected in series (positive to negative), which multiplies voltage by the number of units or parallel (positive to positive, negative to negative), which multiplies AH by the number of units. Series and parallel connections can be combined to produce a battery of just about any size. Stand-by Power and alternative energy systems usually operate at 12, 24, or 48 Volts DC.
Six Volt Deep Cycle golf cart batteries are the most widely used and therefore have the best cost benefit ratio for small installations. They are available with 200 - 350 AH ratings at the 20 hour rate. Golf cart batteries will last from 500 - 850 deep cycles, which usually means 4 - 6 years of operation before their capacity drops off.
Industrial batteries are available in groups of 2 Volt cells which can be strung together in series to create any desired voltage and are available in 500 AH to many thousands of AHs at the 20 hour rate. Industrial batteries can sustain 1500 or more deep cycles and typically last 15 - 20 years.
Temperature Effects on Capacity
The ideal temperature for a lead acid battery is 80 degrees Fahrenheit. Extreme cold and heat affects both capacity and charging characteristics. For example cold reduces capacity. using the 20 hour rating, the following adjustment multipliers can be used to estimate capacity:
|
temperature | factor |
| 50 degrees Fahrenheit | times .85 |
| 30 degrees Fahrenheit | times .75 |
| 20 degrees Fahrenheit | times .65 |
| 0 degrees Fahrenheit | times .55 |
In cold climates the overall size of storage batteries must be increased to maintain the desired capacity. Batteries should be protected from temperature extremes but they also require good ventilation.
The Importance of Ventilation
A battery must be charged at higher than its rated voltage in order to be fully charged. At the end of every charge there is a gassing period when batteries release hydrogen and oxygen. These gasses can be a very explosive, for this reason there should always be good ventilation in a battery storage room.
Lead acid batteries are environmentally friendly. Deep Cycle batteries are nearly 100% recyclable and all battery manufacturers have buyback and remanufacturing programs which effectively keep lead out of the environment.
| 
