What is battery depth of discharge (DoD)?
Depth of discharge (DoD) is the percentage of a battery's total capacity that has been used, measured from full charge. Higher DoD percentages reduce battery lifespan, so most lithium batteries are rated for optimal performance at 80% DoD or lower.
Depth of discharge refers to how much of a battery's stored energy you can draw out before the battery needs recharging. It is expressed as a percentage of the total capacity. A battery with 10 kWh capacity and 80% DoD allows you to use 8 kWh of that energy, while the remaining 2 kWh stays in reserve.
DoD directly impacts how long a battery lasts. Lithium-ion batteries used in most residential solar systems degrade faster when cycled at high discharge depths. Running a battery to 100% DoD (completely flat) before each charge ages it much faster than keeping discharge at 80% or lower. Manufacturers typically rate battery lifespan based on a specified DoD cycle. For example, a battery may be warranted for 10,000 cycles at 80% DoD but only 5,000 cycles at 100% DoD.
For Perth homes and businesses installing solar battery storage, understanding DoD matters because it determines your actual usable capacity. A 15 kWh battery limited to 80% DoD provides only 12 kWh of available energy per cycle, though you pay for the full 15 kWh. Balancing higher usable capacity against longer battery life is a key consideration when sizing a system. When evaluating battery storage options, check both the total capacity and the recommended DoD to compare true available energy and expected system lifespan.