Calculate usable battery capacity based on total capacity and depth of discharge. Compare lead-acid vs lithium usable energy for solar storage.
Depth of discharge (DoD) is the percentage of a battery's total capacity that can be utilized before recharging. It directly determines the usable energy you get from a battery. A 20 kWh battery with 50% DoD gives only 10 kWh of usable energy, while the same battery with 80% DoD provides 16 kWh.
Different battery technologies have very different recommended DoD limits. Lead-acid batteries should not exceed 50% DoD to maintain reasonable cycle life. Lithium iron phosphate (LiFePO4) batteries can safely reach 80–90% DoD with minimal impact on longevity. Going beyond the recommended DoD dramatically shortens battery life.
This calculator helps you understand the real usable energy for any battery by applying the appropriate DoD. This is essential for accurate solar storage sizing — the rated capacity on the label is not what you actually get to use.
By calculating this metric accurately, energy analysts gain actionable insights that inform equipment selection, system design, and operational strategies for maximum efficiency and savings.
Battery manufacturers advertise total capacity, but usable capacity is always less. Knowing the difference prevents undersizing your storage system and running out of power when you need it most. Precise quantification supports regulatory compliance and sustainability reporting, ensuring that energy data meets the standards required by auditors and industry certification bodies.
Usable kWh = Total kWh × DoD Reserved kWh = Total kWh × (1 − DoD)
Result: 16.0 kWh usable, 4.0 kWh reserved
A 20 kWh battery with 80% DoD provides 20 × 0.80 = 16.0 kWh of usable energy. The remaining 4.0 kWh is reserved to protect battery health and maintain longevity. This is a typical configuration for lithium solar batteries.
Lead-acid (flooded): 50% DoD, 500–1,200 cycles. Lead-acid (AGM/gel): 50% DoD, 500–1,000 cycles. Lithium NMC: 80–90% DoD, 3,000–5,000 cycles. Lithium LFP: 80–90% DoD, 5,000–8,000 cycles. Saltwater: 100% DoD, 3,000+ cycles.
For the most accurate storage estimate, multiply rated capacity by DoD and then by round-trip efficiency. A 10 kWh battery at 80% DoD and 90% efficiency delivers 10 × 0.80 × 0.90 = 7.2 kWh to your loads per cycle.
Many inverters let you set a reserve percentage for outage backup. Setting a 20% reserve on a 13.5 kWh Powerwall means only 10.8 kWh is available for daily cycling, with 2.7 kWh held for emergencies. Adjust this setting based on your outage risk.
Fully discharging any battery causes chemical stress that degrades the electrodes. For lead-acid, deep discharges cause sulfation. For lithium, it increases thermal stress. Limiting discharge depth extends cycle life by 2–5 times.
The Tesla Powerwall 2 has 13.5 kWh usable out of approximately 14 kWh total, representing about 96% DoD. Tesla manages the depth of discharge internally, so the 13.5 kWh specification is the actual usable amount.
Higher DoD shortens cycle life. A lead-acid battery at 50% DoD may last 1,200 cycles, but at 80% DoD only 400 cycles. Lithium batteries are more resilient: 80% DoD may yield 4,000+ cycles while 100% DoD yields 2,000–3,000 cycles.
Almost. Usable capacity is limited by DoD, but round-trip efficiency further reduces delivered energy. A 16 kWh usable battery with 90% round-trip efficiency delivers about 14.4 kWh to your loads. The rest is lost as heat during charging and discharging.
For daily cycling, 50–70% DoD maximizes battery longevity. Many home battery systems automatically limit DoD to 80–90% and manage the remaining capacity for backup reserve. If outage protection isn't critical, limiting to 70% DoD extends battery life.
Yes. Cold temperatures reduce available capacity — a battery in freezing conditions may only deliver 60–70% of its rated capacity. Heat accelerates degradation. Most home batteries have built-in thermal management and should be installed in temperature-controlled spaces.