How to Calculate the Depth of Discharge of a Maintenance-Free Lead-Acid Battery?

Calculating the depth of discharge (DOD) of a maintenance-free lead-acid battery involves determining the percentage of the battery’s capacity that has been utilized during a discharge cycle. This calculation requires knowledge of the battery’s nominal capacity and the amount of charge withdrawn from the battery during its use.

1. Determine Nominal Capacity (C_nom): Find the nominal capacity of the battery, which is typically provided by the manufacturer and expressed in ampere-hours (Ah). This value represents the total amount of charge the battery can deliver under specific conditions.
2. Measure Discharged Capacity (C_dis): Determine the amount of charge withdrawn from the battery during its discharge cycle. This can be measured directly using a battery monitoring system, a multimeter, or by integrating the current drawn from the battery over time.
3. Calculate Depth of Discharge (DOD): Use the following formula to calculate the depth of discharge:DOD=Cdis/Cnom​​​×100%
   • Cdis​ is the discharged capacity of the battery in ampere-hours (Ah).Cnom​ is the nominal capacity of the battery in ampere-hours (Ah). Multiply the result by 100 to express DOD as a percentage.
   For example, if a 100Ah battery has discharged 80Ah of charge during a cycle, the depth of discharge would be: DOD=80Ah/100Ah​×100%=80%This means that 80% of the battery’s nominal capacity has been utilized during the discharge cycle.
4. Interpretation: The depth of discharge indicates how much of the battery’s capacity has been consumed during its use. Higher DOD values mean that a greater percentage of the battery’s capacity has been utilized, which can affect battery lifespan and performance. To optimize battery life, it’s generally recommended to avoid deep discharges and keep DOD levels within a certain range, typically less than 80% for lead-acid batteries.