DEEP CYCLE BATTERIES |
2. WHY BOTHER?
Because only the rich can afford cheap batteries..... A good quality deep cycle lead acid battery will cost between $50 and $200 and, if properly maintained, will give you at least 150 deep discharge cycles. The purpose of a deep cycle battery is to provide power for trolling motors, golf carts, fork lift trucks, uninterruptible power supplies (UPS), and other accessories for marine and recreational vehicle (RV), commercial and stationary applications. Dead batteries almost always occur at the most inopportune times: across the lake, during bad weather, or on the 17th tee.
2.1. How is a battery made?
There is an excellent description of how battery is made on the Battery Council International (BCI) web site at
After the "curing" of the plates, they are made up into cells, the cells inserted into a high-density tough polypropylene or hard rubber case [#1 in the diagram above]. The cells are connected to the terminals [#5 in the diagram above], and the case is covered and filled with a dilute sulfuric acid electrolyte [#4 in the diagram above]. The battery is initially charged or "formed" to convert yellow Lead Oxide (PbO or Litharge) into Lead Peroxide (PbO2), which is usually dark brown or black. The electrolyte is replaced and the battery is given a finishing charge. Some batteries are "dry charged" meaning that the batteries are shipped without electrolyte and it is added and recharged when they are put into service.
Two important considerations in battery construction are porosity and diffusion. Porosity is the pits and tunnels in the plate that allows the sulphuric acid to get to the interior of the plate. Diffusion is the spreading, intermingling and mixing of one fluid with another. When you are using your battery, the fresh acid needs to be in contact with the plate material and the water generated needs to be carried away from the plate. The larger the pores or warmer the temperature, the better the diffusion.
2.2. How does a battery work?
A more detailed description of how a battery works can be found on the BCI web site at
2.3. Why do batteries die?
In cold climates, a battery normally "ages" as the active positive plate material sheds (or flakes off) due to the expansion and contraction that occurs during the discharge and recharge cycles. A brown sediment, sludge or "mud," builds up in the bottom of the case and can short the cell out. In hot climates, additional causes of failure are positive grid growth, positive grid metal corroding in the electrolyte, negative grid shrinks, plates buckling, and loss of water. Deep discharges, heat, vibration, over charging, under charging and non-usage accelerate this "aging" process. Another major cause of premature battery failure is lead sulfation. Please see Section 12 for more information on sulfation. Using tap water to refill batteries can produce calcium sulfate, which also will coat the plates and fill pores. Recharging a sulfated battery is like trying to wash your hands with gloves on. When the active material in the plates can no longer sustain a discharge current, and the battery "dies."
Most of the "defective" batteries returned to manufacturers during free placement warranty periods are good. This suggests that most sellers of new batteries do not know how to or fail to take the time to properly load test or recharge them.