Depth of Discharge & Battery Lifespan

What is Depth of Discharge and how does it affect the lifespan of batteries?

Batteries are fast becoming an important part of off-grid and hybrid systems. There are numerous factors that affect the lifespan of a battery but we will be discussing Depth of Discharge today.


What is Depth of Discharge?

Depth of discharge (DoD) simply refers to the degree to which a battery is discharged in relation to its total capacity. When a battery discharges completely, its Depth of Discharge is 100%. If you have a battery that holds 4kWh and you discharge 2.8kWh, the Depth of Discharge is 70%.

The battery life or lifespan is dependent on how deep a battery is cycled each time. A battery ‘cycle’ is one complete discharge and recharge cycle. A battery completes a cycle life when it discharges 100%. Therefore, If a battery is discharged to 50% and recharged, it has completed half cycle. Discharging it to 50% again and recharging it again results in one complete cycle — 100%.

A battery may have 10,000 cycles at 10% DoD but only 2000 cycles at 80% DoD. A battery that is drained to 30% DoD daily will have a longer lifespan than one that is frequently drained to 80% DoD. Frequent charge and discharge of batteries shorten their lifespan.

Most battery manufacturers indicate in the specification sheet the maximum recommended DoD for peak performance of the battery. If the manufacturer of a 10 kWh battery recommends a maximum DoD of 50%, it means that you should avoid discharging more than 5kWh without recharging.

Do you have any questions or comments regarding solar power, inverter, batteries, mini-grid? We’d be glad to hear you out. Join us next week Wednesday on #LearnWithHHS for another interesting chat. Let’s share knowledge.

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