The biggest search on this topic is a permission question — “can I charge my solar battery with off-peak electricity?” — which says something lovely about how under-used Britain’s batteries are: thousands of households own the most profitable setting in home energy and have never switched it on. This is the owner’s guide to switching it on properly. (Still deciding whether to buy a battery for this? That’s our battery-without-solar guide — this page assumes the box is on your wall.)

Yes, your battery can do this — it’s a setting, not hardware

Grid-charging is built into essentially every modern system: hybrid inverters and AC-coupled batteries alike can fill from the grid as readily as from panels. GivEnergy, Fox ESS, Tesla Powerwall, SolaX, Sunsynk, Pylontech, myenergi’s Libbi, and BYD packs on Fronius-class inverters — all of them do it, because the manufacturers know the tariff arbitrage case as well as anyone. If your battery has never grid-charged, the likeliest reason is simply that the installer left the setting off (standard practice when a home has no time-of-use tariff at install time) — which is why so many owners assume they lack the feature. The genuine prerequisites are two: a smart meter doing half-hourly readings, and a tariff with a window worth filling from — the 7–8p overnight rates of EV-style tariffs like Intelligent Octopus Go being the benchmark (and no, you don’t need an EV for the battery to enjoy the window’s whole-house cheap rate on that tariff’s scheduled slots — though eligibility needs its compatible kit; the tariff review covers the routes in).

The arbitrage maths — one subtraction, one haircut

The subtraction: day rate minus off-peak rate = your gross spread. Against a ~26p standard unit rate (the Ofgem cap level) and a 7–8p overnight window, that’s ~18p per kWh. The haircut: round-trip efficiency — batteries return 85–90% of what you put in — trims the net to ~15–16p per usable kWh. Scaled: a 10kWh battery cycled nightly moves £1.50–£1.80 of value per night, £450–£650 a year, stacked on top of whatever your solar already earns. The decision rule that falls out: arbitrage is clearly worth running when your spread beats ~15p (every mainstream EV tariff qualifies), marginal below 10p, pointless on a flat tariff. Two honesty notes from our tariff reviews: EV tariffs carry day rates above the cap, so heavy-daytime households should compare whole bills before switching; and the annual figure assumes the battery’s capacity actually gets used daily — sizing and arbitrage strategy are one decision, because an oversized battery half-cycled earns half the number.

The three settings — and where each brand hides them

Every brand’s version reduces to the same trio: a charge window (set it to your tariff’s cheap hours — 23:30–05:30 on Intelligent Octopus Go), a target state of charge (the seasonal rule below decides the number), and a minimum reserve (10–20%, protecting cells and keeping blackout backup). By brand: GivEnergy calls it Timed Charge — and its direct Octopus integration automates the whole dance, cheap slots included; Fox ESS uses charge periods plus a min-SoC field; Tesla Powerwall runs it through Time-Based Control once you’ve entered your tariff hours; SolaX exposes force-charge periods; myenergi’s Libbi is tariff-aware natively; and BYD packs configure through their paired inverter’s settings rather than the battery itself. The tariff-integrated tier — GivEnergy-Octopus, Libbi with Intelligent Go, and the growing set of price-aware integrations — is genuinely set-and-forget: the system reads tomorrow’s prices and solar forecast and does the arithmetic below for you, which is worth knowing before you build spreadsheet habits the software has already automated.

The seasonal rule: charge the gap

The catches: wear, losses, and the export rule that surprises people

Cycle wear: nightly arbitrage takes a battery from ~250 cycles a year toward the full 365 — real, and designed-for: modern LiFePO4’s 6,000–10,000-cycle ratings hold 16–27 years of daily cycling. The small print worth reading is the warranty’s throughput and cycle caps, which heavy arbitrage reaches years before the calendar does — not a reason to skip the £450–£650, but a reason to favour brands publishing generous throughput numbers. Losses: the 10–15% round trip is already in our maths; distrust any guide quoting the gross spread as profit. The whole-bill test: EV tariffs’ premium day rates mean heavy-daytime homes must compare complete bills — the same catch our IOG review weighs. And the export rule: the tempting endgame — charge at 7p, export at 12–15p — mostly doesn’t work: SEG and export tariffs generally require exported power to be your own renewable generation or exclude grid-charged “brown” export outright (our export tariff review touches the terms). A few specialist flexibility schemes do pay for battery export, but they’re specific products with their own contracts. The profitable, compliant version keeps cheap power in the house — where it earns the full 18p spread anyway, more than any export margin offered.

Frequently asked questions