Battery Life
Service life
Batteries store power using a chemical reaction, and service life is how long the chemical components that make up this reaction are estimated to last. The service life provides a “hard cap” to the maximum amount of time a battery can last, regardless of how it is used. Once the battery reaches the service life, the internal chemistry will start to fail and the battery will no longer operate. Temperature can have a big influence on service life with higher temperatures shortening a batteries service life.
Cyclic Life
The number of cycles that a battery can tolerate is known as the cyclic life. Typically, batteries will be rated to perform a number of cycles at a certain depth of discharge. Once reaching that number, the battery should still be usable, but it will have degraded to about 80% of its original capacity. The number of cycles a battery can perform is directly related to how deep it is discharged on each use (the Depth of Discharge), because performing deep discharges regularly shortens the lifespan of the battery significantly.
Example: Ritar DC12-120S 120Ah AGM Deep Cycle Battery is rated to ~1400 cycles at 30% depth of discharge, but only ~500 cycles at 80% depth of discharge.
BATTERY DAMAGE
Sulfation
During battery use, sulphate crystals form inside the battery as a by-product of the chemical reaction. When the battery is charged again, these crystals are removed. However, if the battery is left in a discharged state and not charged for some time, these crystals become permanent. This reduces the active material within the battery, decreasing battery capacity and performance.
Sulfate also forms in a battery that is constantly being cycled in the middle of its capacity range, somewhere between 80% charged and 80% discharged and is never recharged to 100%. If the battery is continually cycled in this manner, it will lose more and more of its capacity until it no longer has enough capacity to perform the task for which it was intended.
Gassing, Venting, Gassing off
If the safety valve of a battery is activated to relieve pressure, hydrogen gas will escape from the battery into the outside air. This process is knowing as “gassing off”, and typically happens when the battery has been overcharged. Accompanied by the gas release is foul smell. If gassing off happens, the battery performance will be reduced as some of its chemistry has been lost by the gas leaving the battery.
Overcharge
When a battery is charged at too high a voltage, or continually charged even when it is at full capacity, it will become overcharged. This can cause the battery to swell in size and gas off, reducing capacity and potentially creating a dangerous situation.
Undercharge
If too low a charge voltage is applied to a deep cycle battery, the current flow will slowly trickle away and basically stop before the battery reaches full charge. Over time this will eventually reduce capacity due to small amounts of lead sulphate remaining on the electrodes.
Thermal Runaway
If a battery is significantly overcharged, it may cause a dangerous situation called thermal runaway. This is where the battery is progressively heated up from the overcharge, and as it gets hotter it will accept more current, heating it up even further. Eventually catastrophic failure will occur such as meltdown of the cell, explosion or fire.
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