Choosing a Home Battery for a Smart or Time-of-Use Tariff
- Fixed-window tariffs such as Go and Cosy need a battery that can fill within the cheap period.
- Half-hourly tariffs such as Agile need software that can follow changing prices, or an API you can use.
- Supplier pages we read describe cars, heat pumps and smart devices, and do not confirm battery eligibility, so ask.
- A smart meter that the supplier can connect to is required for these tariffs.
- Round-trip losses and the standing charge limit what the cheap rate can save.
If you are buying a battery mainly to use a smart or time-of-use tariff, the tariff shapes the shopping list: how fast it can charge, how well its software follows prices, and whether your supplier and the battery will actually work together.
Match the battery to the shape of the tariff
At the time of writing, Octopus's own pages describe four common shapes. Octopus Go has a cheap window from 00:30 to 05:30. Intelligent Octopus Go has an off-peak window from 23:30 to 05:30 and up to six hours of smart charging a day at the off-peak rate. Cosy Octopus has three cheaper periods (04:00 to 07:00, 13:00 to 16:00 and 22:00 to 00:00) with a peak from 16:00 to 19:00, where the cheap rate is 51% below the day rate and the peak is 50% above it. Agile Octopus prices change every half hour and are published daily, with a cap of 100p/kWh.
Those are Octopus's published descriptions and tariffs change, so check the current page for your region. For the background on how fixed windows differ from half-hourly pricing, see time-of-use tariffs explained.
Check the charge and discharge power
A cheap window is only useful if the battery can fill within it. As simple arithmetic, a battery that charges at 3 kW can move at most about 15 kWh in a five-hour window before losses, while one at 2 kW across a three-hour Cosy period can move about 6 kWh. These are illustrations, not product figures.
Discharge power matters too, because the battery has to cover your evening peak. If it cannot supply the load, the house imports from the grid at the dearer rate. Look for continuous charge and discharge power on the datasheet, and see our guide to how to read a home battery datasheet and C-rate explained.
Scheduling, software and supplier integration
The cheapest tariff does little if the battery charges at the wrong time. Look for scheduled grid charging with start and end times you can set yourself, a target charge level, and a clear way to change both. Half-hourly tariffs need more: the battery must either follow prices itself or be controlled through an integration.
Octopus says you can use its Agile API to program smart devices and lists partner brands for smart home devices, but the page does not say which batteries work with it. Its Go, Intelligent Octopus Go and Cosy pages describe cars, chargers and heat pumps and do not address home batteries either. We could not confirm battery eligibility from those pages, so ask both the supplier and the battery maker in writing which tariffs and which control method are supported for your model.
Good to know
Ask the installer to set up the tariff schedule at commissioning and to show you where it lives in the app, so you can change it if the cheap windows move.
Losses, standing charges and winter prices
Every kWh that goes in and comes back out loses some energy as heat, so the gap between cheap and dear rates has to be wider than the loss. Our guide to round-trip efficiency shows the arithmetic. A battery also cannot reduce the standing charge, which does not depend on how much you use.
On Agile, Octopus's own page warns that a standard tariff may be cheaper in winter when prices have been high, and says to check current prices before deciding. A battery makes it easier to avoid the peak, but it does not make every day cheap.
What to check before you sign
These tariffs only work with a smart meter that the supplier can connect to remotely. Octopus's pages say that means a SMETS2 meter or a Secure SMETS1 meter, and that connection takes about 14 days. Our guide to smart meters and half-hourly settlement explains the wider picture.
- Can I set grid charging by time and by target level in the app?
- Does the battery have a documented link to my chosen tariff or supplier?
- What are the continuous charge and discharge power ratings?
- How is the backup reserve set, and does it reduce the energy available for the tariff?
- Which smart meter do I have, and can the supplier connect to it?
Common questions
Which tariff is best for a home battery?
It depends on your use and on what the tariff and your battery support. Fixed cheap windows are simpler to plan around, while half-hourly prices need better software. Check the supplier's current terms.
Do I need a smart meter for a time-of-use tariff?
Yes. Octopus's tariff pages say it needs to be a SMETS2 meter or a Secure SMETS1 meter that it can connect to.
Can any home battery use Intelligent Octopus Go?
We could not confirm that from Octopus's page, which describes eligible cars and chargers and does not mention batteries. Ask the supplier and the manufacturer.
Will the battery save money on Agile in winter?
Not automatically. Octopus's page notes that prices have been high at times and that a standard tariff may be cheaper in winter, so check current prices.
Related guides
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