Yes, a home battery can be charged from the grid overnight if the battery, inverter and installation support that operating mode. Whether it is worth doing depends on more than the headline night rate: the price spread after documented battery losses, how much energy the cheap window can actually move, and whether grid charging leaves enough room for solar or gives up valuable export income.
The useful order is simple: test the delivered cost of the off-peak electricity first, then the charging window, then the solar/export trade-off, and finally the control setup. For the full investment calculation, use our UK home battery payback guide.
In short
Overnight grid charging can reduce the energy cost of electricity you use later, but only when the battery supports grid charging and the off-peak electricity remains meaningfully cheaper after documented losses. You also need enough charging time and battery headroom, plus later household demand that would otherwise be met at a higher import rate. Solar generation, export value and tariff-control rules can change the answer.
The simple test: is the price spread wide enough?
Do not compare the cheap import rate with the later import rate and stop there. A battery returns less energy than it takes in, so the operating comparison should use the cost of electricity actually returned from the battery, based on the documented loss or efficiency figure for the system you are assessing.
Start with the delivered cost of overnight electricity
Operating price-spread formula
Effective stored-energy cost = off-peak import price ÷ documented round-trip efficiency
If the off-peak price is Poff and the documented round-trip efficiency is η expressed as a decimal, the effective cost of each kWh returned from the battery is Poff ÷ η. Compare that with the later import price Plater that the battery would genuinely displace.
There is no universal p/kWh threshold. If a documented system efficiency is not available, do not substitute a generic percentage simply to complete the calculation.
A positive headline spread is not enough by itself. The battery must later discharge into household demand that would otherwise have been imported at the higher rate. If the effective stored-energy cost is similar to that avoided import price, the tariff spread may be too small to make that energy shift worthwhile.
See how solar, the battery, household demand and the grid interact in our storage basics guide.
Keep daily tariff maths separate from full battery payback
This price-spread test answers a narrow operating question: does shifting a particular unit of electricity from a cheaper period to a dearer one make sense under the stated assumptions? It is not a full investment calculation. Battery purchase cost, installation cost, degradation, warranty conditions, long-term utilisation and future tariff changes belong in the separate payback assessment.
Which UK tariffs can work with overnight battery charging?
The tariff type changes how predictable the cheap period is and how much scheduling work is needed. Energy Saving Trust distinguishes Economy 7, dynamic tariffs and other time-of-use arrangements, including solar/battery tariffs with separate import and export pricing. Energy Saving Trust’s tariff guidance is useful for the category definitions; your actual decision should use your own current tariff terms.
Economy 7
Ofgem says Economy 7 provides seven off-peak hours, with the exact period given when you sign up. The hours can vary by location and supplier, and the daytime rate is higher, so the decision should consider your whole consumption pattern rather than the night rate alone. Ofgem also notes that households using little electricity at night may be better off on a single-rate tariff. Read Ofgem’s Economy 7 guidance.
Fixed time-of-use tariffs
A fixed time-of-use tariff can be straightforward for battery scheduling because the cheaper and dearer periods are defined in advance. The relevant comparison is still the same: use the current off-peak import price, adjust for documented battery losses, and compare it with the import price the stored electricity would actually replace later.
Dynamic tariffs
Dynamic tariffs can create wider or narrower spreads from one day to the next because the price can change every half-hour. That makes control more important, but it does not prove that a particular battery automatically follows the tariff. Confirm the schedule or integration your system actually supports, and re-check the economics when tariff conditions change.
Check the charging window, not just the cheap rate
Even an attractive off-peak rate is of limited use if the battery cannot move enough energy during the cheap period. The first physical check is power multiplied by time.
Capacity is kWh; charging power is kW
Capacity in kilowatt-hours (kWh) describes how much energy can be stored. Charging power in kilowatts (kW) describes how quickly energy can enter the battery. A battery with enough capacity can still fail to make full use of a short cheap period if its supported charging power is too low for the energy you are trying to move.
How much energy can the cheap window actually move?
Supported charge power (kW) × cheap-window length (hours) = theoretical charging-energy ceiling (kWh). This is only a ceiling. The battery’s starting state of charge, available capacity, conversion losses, reserve settings, control limits and other operating conditions can reduce the energy actually stored and returned.
If an EV or heat pump also uses the cheap period, include that demand in the household schedule. The aim is not to reserve every off-peak unit for the battery, but to avoid assuming that the same cheap window can satisfy several flexible loads without checking how you intend to prioritise them.
What changes if you also have solar panels?
Solar changes the opportunity cost of filling the battery from the grid. The same overnight schedule may be more useful before a low-generation day and less useful when you expect enough solar surplus to fill the battery later.
Leave room for tomorrow’s solar
If the battery is full in the morning, there may be less headroom for solar surplus later in the day. Before setting a routine overnight charge, compare the expected need for stored grid electricity with the solar energy you are reasonably likely to have available. The right state-of-charge target can therefore be seasonal or day-specific rather than fixed all year.
Compare storing solar with exporting it
Solar electricity is not automatically “free” to store if it could otherwise have been exported for payment. When solar would be exported, the opportunity cost of storing it is the export income you give up. That means your decision can involve three values at once: the cost of grid charging, the later import price you might avoid, and the export value of solar you might otherwise sell.
Do not assume battery exports automatically qualify for SEG
The Smart Export Guarantee (SEG) applies to eligible small-scale low-carbon generation in Great Britain. Ofgem lists solar PV, wind, micro-CHP, hydro and anaerobic digestion as the eligible generation technologies; battery storage itself is not one of those listed generation technologies. SEG licensees set their own rate, contract length and other terms. Check Ofgem’s current SEG guidance and your export supplier’s terms rather than assuming electricity previously charged into a battery from the grid will receive SEG payment.
Automation helps — but keep control of the rules
Automation is most useful after you have defined the decision rules: when charging is allowed, how much battery headroom to preserve, which import periods to avoid later and what reserve settings matter for your household. It should not turn an untested tariff spread into an assumed saving.
User-controlled and supplier-controlled charging
As of 26 August 2026, British Gas distinguishes between a battery tariff where the customer controls the charging routine and offers where the supplier manages the battery schedule. This is one supplier example, not a market-wide rule. See the current British Gas battery-tariff terms.
Whichever model you use, verify who controls the schedule, whether you can change it, what tariff or metering conditions apply, and what happens when your tariff changes. Do not assume a dynamic tariff and a battery are automatically integrated simply because both are described as “smart”.
Coordinate the battery with EVs, heat pumps and reserve settings
If several flexible loads share the same cheap period, decide which one gets priority and how much energy each actually needs. Also check any minimum reserve or state-of-charge rule that limits how much stored electricity you expect to use later. Review the schedule whenever the tariff window, household routine or seasonal solar pattern changes.
What can you verify for the Sunpura S2400?
The current S2400 specification lists a maximum on-grid AC input power of 2,400 W. That is a product input limit, not a guarantee that every UK tariff or cheap-rate window will suit the system.
Automatic use with a particular tariff depends on the tariff, metering setup and the control integration available for the installation. This guide does not make named UK supplier-compatibility claims. It also does not use a numeric S2400 round-trip-efficiency figure because the current public product documentation does not provide one.
Checking S2400 for your tariff setup?
Use the product specification together with your current tariff window, metering setup and the control options validated for your installation.
Check S2400 specifications and control optionsOvernight battery charging checklist
Check these seven points before setting a routine
If you do not have solar panels, assess the battery-only case separately before treating tariff arbitrage as a reason to buy a battery. The overall purchase decision belongs in a broader household economics assessment rather than this daily charging rule.
