Why is Depth of Discharge important? What does it mean?
“DoD,” or “Depth of Discharge,” is a term used to define how deeply a battery is or should be discharged. When we say a battery is completely charged, we mean that its DOD is 0%.
When a battery has supplied 30% of its energy and still has 70% remaining, it is said to be at 30% DOD. A fully charged battery has a DOD of 100%.
Depth of discharge and cycle life
The majority of battery chemistries, including lead-acid and lithium-ion, degrade when they are charged and used up, eventually losing their capacity to store energy..
This influences the battery’s operational life as well as the total number of hours it can store over its lifetime.
This has an impact on the battery’s capacity to store hours overall as well as how long the battery can operate for.
Let us consider two factors out of other factors that can cause this:
- The number of discharge-recharge cycles, and
- The maximum depth to which they are discharged.
If a lead-acid battery is drained/used to 100% of its power storage capacity every time it is used, its electrolyte may quickly degrade and the battery may not be able to retain energy as well as it did to when it was only discharged to a maximum of 50%.
On battery information boards, the term ‘cycle life or cycles’ (with the qualifier ‘at X% DoD’) is used.
Depth of discharge (DOD)
All battery manufacturers recommend to keep the Depth of Discharge (DOD) below the maximal limit of 100%. Ideally 80% DOD or less is recommended. This means that when using your battery, you should ensure that only less than 80% power capacity is used before recharging again.
In fact, because it is preferable to avoid deep cycle discharging, it appears to be preferable to charge as frequently as possible. “Charge (to full) before usage” is preferable to “empty and charge.”