What is depth of discharge?
Depth of discharge describes how far a battery has been discharged, expressed against a stated capacity reference. An assumed 80% discharge of 100 kilowatt-hours means 80 kilowatt-hours removed before conversion losses. Deeper cycling can affect ageing [S1], so check the permitted operating window and warranty rather than choosing by headline capacity alone. Checked October 2026.
What is depth of discharge in a battery?
Depth of discharge, often shortened to DoD, describes how much of a battery’s stated capacity has been used. It matters when comparing the energy your site can draw with the large capacity figure on a proposal. The government’s storage review identifies deeper discharge as a potential contributor to faster battery ageing [S1].
Ask the installer to state the reference capacity and the operating window together. A nominal energy rating, a usable energy rating and a configured reserve should not be treated as interchangeable figures.
How do you calculate the energy in a discharge window?
Illustration, not a quote: assume a battery has 100 kilowatt-hours (kWh) of available capacity, begins fully charged and stops discharging at 20%. The available window is 100% − 20% = 80%. The simplified energy calculation is 100 kWh × 0.80 = 80 kWh, before conversion and auxiliary losses.
These are assumed settings, not recommended limits. SAM’s dispatch guidance explains minimum and maximum state of charge settings and notes that their capacity reference changes as the battery degrades [S2]. Ask your installer for the energy delivered at your site connection, using the proposed equipment and operating limits.
How does a depth of discharge limit affect your site?
Request a daily operating plan that shows the reserve needed for your intended use. If backup power matters, ask how the controls retain that reserve while meeting your normal demand. Have the installer confirm both the available energy and the power the system can deliver.
Compare battery sizing with warranty and degradation terms. Read state of charge for the remaining-charge measure and round-trip efficiency for energy losses.
Next step
Get matched with an installer that covers your area. Piggy Pineapple Ltd operates this referral service. We refer enquiries to installer partners and may be paid a fee. Our owner holds shares in at least one partner. Before sharing your details, we name the proposed partner and disclose any shareholding in it.
Common questions
What does an 80% depth of discharge mean?
In a simplified energy illustration, removing 80 kWh from a stated 100 kWh full capacity is 80% depth of discharge. Confirm the capacity reference and permitted limits in the product documents [S1][S2].
Is there one maximum depth of discharge for every battery?
Do not apply a universal setting. Ask for the manufacturer's operating limits and warranty conditions. The government's storage review identifies depth of discharge as a factor in battery ageing [S1].
Can the available capacity change over time?
Yes. SAM's modelling guidance explains that available capacity changes as a battery degrades. Confirm whether a proposal's operating percentages refer to current available capacity or nominal capacity [S2].
Ask about your site
Sources
- Environmental and social implications of energy storage technologies, Department for Energy Security and Net Zero,Last checked 16 October 2026
- Battery Dispatch FOM, National Laboratory of the Rockies - System Advisor Model,Last checked 16 October 2026