Depth of discharge (DoD) describes how much of a battery’s stored energy you’re allowed to use in a single cycle. A 13.5 kWh battery with 100% DoD gives you all 13.5 kWh. One with 80% DoD gives you 10.8 kWh, holding 20% in reserve to protect the cells.
Battery chemistry determines how much cycling a cell can tolerate. Lithium iron phosphate (LFP) batteries, used in several home storage products, handle frequent deep cycling better than some other lithium chemistries. This is part of why LFP products often advertise higher DoD ratings. Nickel manganese cobalt (NMC) batteries may perform slightly better at peak output but are often rated at a lower DoD to preserve cycle life.
For comparing home battery quotes, the number that matters most is usable capacity in kWh, which already accounts for DoD. A battery rated at 15 kWh total with 90% DoD gives you 13.5 kWh usable — the same as a 13.5 kWh battery at 100% DoD. The spec sheet doesn’t always make this easy to find, so ask for the usable kWh figure directly.
When you’re getting quotes
Request the usable capacity in kWh for each battery being quoted, not just the total rated capacity. Ask whether the DoD is fixed or user-adjustable. Some systems let you set a minimum reserve (for example, keeping 20% back for grid outages while using 80% for daily time-of-use shifting). This flexibility can matter if you want the battery to serve dual purposes — daily savings and emergency backup.
Common questions
- What is a good depth of discharge for a home battery?
- Most quality home batteries have a usable DoD of 90–100%. The Tesla Powerwall 3 and Enphase IQ Battery 5P are both rated at 100% DoD, meaning the full rated capacity is available for use. Some older or lower-cost batteries reserve 10–20% as a buffer, effectively giving you less storage than the spec sheet suggests. Always compare the usable capacity in kWh, not just the total rated capacity.
- Does depth of discharge affect how long a battery lasts?
- It can, but modern home batteries are engineered to handle their rated DoD over their warranty period. Manufacturers like Tesla and Enphase specify a cycle life (number of charge-discharge cycles) at the rated DoD. Regularly discharging below the manufacturer's recommended DoD — which is harder to do on a managed system — can degrade cells faster. For most homeowners, following the default settings keeps degradation within warranty parameters.
- How does depth of discharge affect backup power during a Duke Energy outage?
- DoD directly determines how long your backup lasts. A 13.5 kWh battery at 100% DoD gives you the full 13.5 kWh to work with. At 80% DoD, you'd only access 10.8 kWh. For a home in Raleigh or Charlotte averaging 40–50 kWh of daily consumption, a single Powerwall covers roughly six to eight hours of normal usage regardless of DoD — which is why many homeowners pair two batteries or combine with solar for extended outage coverage.