Real vs nameplate battery capacity
A battery advertised as “10 kWh” rarely delivers 10 kWh to your loads. Depth of discharge, temperature and round-trip losses all take a cut. Enter the nameplate figure to see what you actually get — the physics the financial comparison sites skip.
Why nameplate ≠ usable
Three deductions stand between the label and your appliances. Depth of discharge: you can only safely use part of the capacity — about 80% for LiFePO4, 50% for lead-acid — or you destroy cycle life. Temperature: capacity drops in the cold, sharply for lead-acid. Round-trip efficiency: some energy is lost charging and discharging, about 4% for LiFePO4 and up to 20% for flooded lead-acid. A “10 kWh” lead-acid battery in a cold space can deliver less than 4 kWh.
Comparison and payback portals usually treat the battery as a flat kWh number, which overstates what you really get. Size and compare on delivered energy instead. For honest payback grounded in this real figure, see the battery payback calculator.
Frequently asked questions
How much usable energy is in a 10 kWh battery?
After depth-of-discharge limits, temperature and round-trip losses, a 10 kWh LiFePO4 battery at room temperature delivers roughly 7.7 kWh to your loads. A 10 kWh lead-acid battery delivers far less, especially in the cold.
Why is my battery's real capacity lower than advertised?
The nameplate kWh is the nominal total. You can only safely discharge part of it (depth of discharge), capacity falls in the cold, and charge/discharge isn't 100% efficient. Real delivered energy is the nameplate minus all three.
Looking for a definition or a quick answer? See the solar & battery glossary for terms used on this page, or the FAQ for common sizing questions.
Sources & standards
- IEC 62619 — Safety Requirements for Secondary Lithium Cells and Batteries for Industrial Applications — International safety-testing standard for LiFePO4 and Li-ion (NMC) cells used in stationary storage.
- IEC 60896 — Stationary Lead-Acid Batteries (test & performance requirements) — International test standard covering VRLA (AGM/gel) and flooded stationary lead-acid batteries.
- Victron Energy — Battery Capacity and the Peukert Exponent — Manufacturer technical explainer on why usable capacity falls at higher discharge (C-)rates.
Educational estimate. See the methodology for the constants and formula.