Total battery capacity is the energy the manufacturer prints on the spec sheet, in kilowatt-hours (kWh). Usable capacity is the share of that total you are allowed to charge and discharge in normal use. Some systems reserve a slice of the pack so the cells are not emptied to empty every cycle.
What it means for a home battery
Your daily saving tracks usable kWh, not the headline total. If a pack is labelled 10 kWh but only 9 kWh is usable, a full overnight charge only shifts about 9 kWh into the day rate window (before round-trip efficiency losses). The Energy Saving Trust measures home battery size in kWh and notes that systems often stop discharging before the pack is empty, which is the same idea as a usable limit.
EcoFlow lists a single-unit capacity of 5,024 Wh for the STREAM AC 5000 on its UK product page (and the same 5,024 Wh figure for the STREAM 5000). Habo's offer is an electrician-wired EcoFlow STREAM from £2,499. Join the waitlist. EcoFlow does not publish a separate usable-capacity percentage for STREAM, so Habo's maths treat about 5 kWh as the energy delivered in a full cycle, then apply the 90% round-trip assumption. See what size battery for how to match usable kWh to the energy you use outside the cheap window.
When you compare quotes, ask for usable kWh on the warranty sheet, then work cost per usable kWh. Also check inverter power in kW vs kWh, depth of discharge, and the payback period. The calculator uses delivered kWh, not a marketing total.
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Frequently asked questions
Many systems keep a reserve so the cells are not emptied fully. That reserve protects cycle life. The usable figure is what you can schedule day to day.
EcoFlow lists a single-unit capacity of 5,024 Wh (about 5 kWh) for the STREAM AC 5000 and STREAM 5000 on its UK product pages. It does not publish a separate usable-capacity percentage.
Divide the installed price by usable kWh, not by the marketing total. Then check round-trip efficiency, warranty cycles and inverter power in kW.
Simple battery, simple install
Electrician-wired EcoFlow STREAM from £2,499. Habo will try to serve anyone who registers in an area where we have an electrician. Nothing to pay today.
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