What is Depth of Discharge (DOD) and how does it affect a battery?
When a battery is discharged, the amount of energy taken out will determine the depth at which it was discharged. For example if you have a 100 amp hour battery and use 50 amp hours you have discharged the battery 50% which means the depth of discharge is 50%. If you took the same battery and discharged it only 20 amp hours or 20% of the battery, your depth of discharge will be 20%. This is an important number to keep in mind, because depending on which type of battery you are using, the number of cycles will be vary based on your depth of discharge.
Most lead acid batteries experience significantly reduced cycle life if they are discharged more than 50%, which can result in less than 300 total cycles. Conversely LIFEPO4 (lithium iron phosphate) batteries can be continually discharged to 100% DOD and there is no long term effect. You can expect to get 3000 cycles or more at this depth of discharge.