General Battery Terminology
Depth of Discharge (DOD)
Depth of Discharge (often abbreviated to DOD or D.O.D) is the percentage amount of a deep cycle battery’s capacity that is used, before charging it back up again.
Example: a 100Ah Capacity Battery used down to 80Ah would be at 20% DOD and if used down to 20Ah, this would be at 80% DOD.
Cycle
A cycle is the process of discharging a deep cycle battery and then recharging it to full. One cycle means that the battery is discharged and then recharged once. Deep cycle batteries are typically rated to a certain number of cycles at a depth of discharge. The number of cycles at a given DOD is key indicator of a batteries value for money
Example: A battery might be rated to perform 1400 cycles at 30% depth of discharge. This means that the battery should withstand being discharged 30% and then recharged to full 1400 times. The same battery might be rated to perform 800 cycles at 50% DOD and 500 cycles at 80% DOD
Internal resistance
Internal resistance is how much a battery “resists” energy flow. Lower is better, allowing charging and discharging at more efficient rates. Most of the loss in charging and discharging batteries is due to internal resistance, and the lost energy is then converted to heat (which is why batteries get hot when they are charging). Many factors can affect internal resistance such as battery age, chemistry and sulfation.
State of charge
The percentage of capacity that a battery is at. Typically, this can be worked out by measuring battery voltage when there are no loads or draws on the battery. The voltage of a battery has often been used to correlate with the state of charge and there are numerous charts attesting to this. However, the type of battery will play a big part in the voltage range over which state of charge is measured.
Some Examples:
An AGM Battery at approx. 12.7 volts is considered 100% fully charged, while an AGM battery at 10.5 volts is considered entirely discharged at 0%. However, a Lead Crystal battery at approx. 12.7 volts is considered 100% fully charged, at 0.0 volts is considered entirely discharged at 0%. Similarly, a Lithium battery at approx. 12.8 volts is considered 100% fully charged and at 11.2 volts (internal low voltage disconnect set point) is considered entirely discharged at 0%
Back to FAQ & Guides
Back to Home