Round-trip efficiency is the percentage of energy you get back out of a battery compared with the energy you put in. If you charge with 10 kWh and later use 9 kWh, the round-trip efficiency is 90%. The missing energy is lost as heat in the battery and the inverter.
What it means for a home battery
On a time-of-use tariff the battery buys cheap overnight electricity and covers daytime use. Round-trip losses mean you must buy a little more overnight than you later avoid at the day rate. Habo's worked example for a 5 kWh EcoFlow STREAM on Octopus Go assumes 90% round-trip efficiency because EcoFlow does not publish a STREAM figure on its UK product pages. Octopus Go needs an EV charged at home (Go terms clause 2.1.3). To deliver 5 kWh you therefore buy 5 / 0.9 = 5.556 kWh overnight.
On Octopus Go 12M Fixed GO-FIX-12M-26-10-14 (checked again on 28 October 2026 via the Octopus API; night 9.4p; day 35.293p in East Midlands to 39.3081p in Merseyside and North Wales; still open with no available_to date), that one-cycle maths is up to about £453 to £527 a year best case (£453.49 to £526.76 before rounding). See how much a home battery can save and the homepage maths. Real savings will be lower if you do not use a full cycle every day.
When you compare quotes, ask for the manufacturer's round-trip efficiency including the inverter, not a cell-only number. A higher efficiency figure improves the saving for the same usable kWh. Pair this with usable vs total capacity and depth of discharge before you trust a payback claim. Run your own rates on the savings calculator. Habo's offer is an electrician-wired EcoFlow STREAM from £2,499. Join the waitlist.
Keep an eye on UK battery prices
Leave your email for occasional updates on UK home battery prices, tariff changes and the 0% VAT deadline. No spam, unsubscribe any time.
Thanks, you're on the list.
Frequently asked questions
Check the manufacturer figure for the exact model, including inverter losses. EcoFlow does not publish a STREAM round-trip efficiency on its UK product pages, so Habo states a 90% assumption where it uses one.
EcoFlow does not publish a STREAM round-trip efficiency on its UK product pages, so Habo's savings maths assume 90% and say so.
Lower efficiency means you buy more cheap overnight units to deliver the same daytime kWh, so the yearly saving falls. Habo's calculator uses the same 90% assumption as the homepage maths.
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.
Join the waitlist