Batteries are divided in two ways, by application (what they are used for) and construction (how they are built). The major applications are automotive, marine, and deep-cycle. The major construction types are flooded (wet), gelled, and AGM (absorbed glass mat).
What is A Deep Cycle Battery? Deep cycle batteries are designed to put out 80% of their capacity time after time without damage. Automotive batteries can be severely damaged if heavily discharged a few times. If discharged 80% and then recharged fully, deep cycle batteries can handle from a few hundred to 1000 complete cycles, where an automotive battery might be able to last for only 30 to 50 cycles. Deep cycle batteries may not work well in automobiles because they are not designed to put out the massive power needed for startup. Many marine and RV batteries are dual purpose - these are deep cycle batteries that will also work as SLI batteries. Nearly all marine and many industrial batteries are sealed and may also be gelled, glass mat, and/or maintenance free. Sealed batteries are not totally sealed - the actual name for them is Valve Regulated Sealed Lead-Acid Batteries, or VRSLB, sometimes called VRLA, or Valve Regulated Lead-Acid.
Sealed Batteries These batteries are made with vents that cannot be removed. Maintenance free batteries are also sealed. Sealed batteries are not totally sealed, as they must allow gas to vent during charging. If overcharged too many times, these batteries can lose enough water that they will die before their time. Most deep cycle batteries use Lead-Calcium plates for increased life, although most forklift batteries use Lead-Antimony. A few industrial batteries have special caps that convert the Hydrogen and Oxygen back into water, reducing water loss by up to 95%. Lead-Antimony batteries have a much higher self-discharge rate than Lead or Lead-Calcium, but the Antimony improves the mechanical strength of the plates, which can be an important factor in electric vehicles. They are generally used where they are under constant or very frequent charge, such as fork lifts and floor sweepers. The Antimony increases plate life at the expense of higher self discharge. If left for long periods unused, these should be trickle charged to avoid damage from sulfation.
Batteries come in all different sizes. Many have group sizes. These specifications are based on the physical case size, terminal placement, type and polarity. In Europe, the European Committee for Standardization has adopted the ETN (European Type Numbering) standard. It is NOT a measure of battery capacity. Typical BCI codes are group U1,24, 27, and 31. Industrial batteries are usually designated by a part number such as ”FS” for floor sweeper, or ”GC” for golf cart. Many batteries follow no particular code, and are just manufacturers part numbers. Other standard size codes are 4D and 8D, large industrial batteries, commonly used in solar electric systems.
These are the standards that most battery companies use to rate the output and capacity of a battery.
Temperature Battery capacity is reduced as temperatures go down. This is why your car battery dies on a cold winter morning. Capacity is increased at temperatures over 25 C (77 F), but battery life is shortened. Battery capacity is reduced by 50% at -22 degrees F. Battery life is reduced at higher temperatures - for every 15 degrees F over 75, battery life is cut in half, for ANY type of Lead-Acid battery, whether sealed, gelled, etc.
Cycles vs. Life A battery cycle is one complete discharge and recharge cycle. It is usually considered to be discharging from 100% to 20%, and then back to 100%. Battery life is directly related to how deep the battery is cycled each time. If a battery is discharged to 50% every day, it will last about twice as long as if it is cycled to 80% DOD. If cycled only 10% DOD, it will last about 5 times as long as one cycled to 50% - but to do so, you would need a very large battery capacity in most cases.
Battery Voltages All Lead-Acid batteries supply about 2.14 volts per cell when fully charged. Batteries that are stored for long periods will eventually lose all their charge, at about 1% to 10% per month. A float charge should be maintained on the batteries even if they are not used. Batteries self-discharge much faster at higher temperatures. The old myth about not storing batteries on concrete floors is just that - a myth. Lifespan can also be seriously reduced at higher temperatures - most manufacturers state this as a 50% loss in life for every 15 degrees F over 77 degrees cell temperature. Lifespan is increased at the same rate if below 77 degrees, but capacity is reduced at lower temperatures at the rate of 10% per 15 degrees F. Most deep cycle Lead-Acid batteries are actually an alloy of Lead and Calcium and/or Lead and Antimony for better plate life.