If the power goes off on your street in Mitcham, a standard home battery goes off with it. That surprises people, and it is the most important thing to know before you weigh up a battery for backup. This guide covers who runs the local network, how often supply is lost in this part of London, and what the connection rules mean for a battery in CR4. For the wider case for a battery here, see our page on battery storage in Mitcham.
The short version: Mitcham’s town centre is on a network whose interruption figures are well below the sector average on Ofgem’s latest data, so for most households here backup is not the reason to buy a battery. The reasons are storing solar and shifting what you buy to cheaper hours. If backup still matters to you, it can be designed in, but it is never there by default.
Who runs the wires in CR4
The distribution network operator, not your energy supplier, owns and maintains the cables to your house. In Mitcham that is UK Power Networks, which owns and maintains the network across London, the South East and the East of England. On its own licence-boundary data, the Mitcham town-centre point we use sits in the London Power Networks licence area, about 1.0 km from the South Eastern Power Networks boundary.
That distance is short enough that some Mitcham addresses may be on South Eastern Power Networks instead. Both are UK Power Networks, the connection rules are the same, and its online area checker confirms which one covers your postcode.
How often the power goes off
Ofgem publishes reliability figures for each licence area every year. For 2024/25, London Power Networks recorded about 11.2 supply interruptions per 100 customers and about 10.5 minutes lost per customer over the year, both inside Ofgem’s targets of 13.4 and 13.6. A year earlier the figures were 12.2 and 11.4.
For comparison, South Eastern Power Networks recorded about 42.2 interruptions per 100 customers and 30.4 minutes in 2024/25, and the sector as a whole about 39.7 and 35.1. These are licence-area averages, not a forecast for your street, and Ofgem notes that severe-weather adjustments were applied before its final assessment, so treat them as reported figures. Read plainly, they say that in the London Power Networks area a power cut is an occasional event, not a routine one.
What a standard battery does in a power cut
A grid-tied solar or battery system is designed to disconnect when the network supply fails. The reason is safety: if a house kept pushing electricity into the street cables during a cut, it could endanger the people repairing them. So in a standard Mitcham installation, the battery stops supplying the house at the same moment as the grid does, however full it is. That holds on London Power Networks and South Eastern Power Networks alike, so it applies to every CR4 address whichever side of the boundary it falls.
A battery provides power during a cut only if the specific system and installation support backup. That means equipment that separates the house from the network before the battery takes over, and a design agreed in advance. It is a choice to make at the quote stage, not something to discover during the first cut, and on a network that lost each customer about 10.5 minutes of supply across 2024/25, the extra cost is the thing to weigh.
If backup matters to you
Some households have a genuine reason to want it: medical equipment, home working that cannot stop, or simply peace of mind. If that is you, tell the installer before any design is drawn up, ask which circuits the backup would cover, and ask what it adds to the cost. On London Power Networks’ 2024/25 figures, most Mitcham households would rarely call on it, which is why we would not recommend paying for backup unless you have a specific need.
G98, G99 and export limits
Every battery needs the network operator to know about it, and for a CR4 home that operator is UK Power Networks, whichever of its two licence areas covers the street. Under the Energy Networks Association’s G98 rule, if all the generation and battery storage at your home adds up to 16 A per phase or less, 3.68 kW on a single-phase supply, a type-tested system is notified before commissioning or no later than 28 days after it. Anything larger needs a G99 application approved before the work starts, and a 4 kW inverter, at 17.39 A, is just over the line.
The battery’s inverter counts alongside any solar, so adding a battery to a modest array can move a Mitcham home from G98 to G99. UK Power Networks says it automatically approves applications where the maximum export, after any export limitation, is under 5 kW, and that there is nothing to pay it unless your supply needs an upgrade first. An export limit, set in the system’s settings, is how a larger system stays under that line.
What this means for a Mitcham terrace or flat
Across the six Mitcham wards, Census 2021 puts 39.9% of households in terraced houses and 30.4% in purpose-built flats, and just under half own their home. On a terrace, the network questions above apply exactly as for any house; the practical question is where the unit goes. In a flat, the freeholder’s or housing association’s agreement comes first, and if panels are not possible, a battery on its own charged on a cheaper overnight tariff is the route to look at. Our guide to how solar battery storage works covers both set-ups.
For the roof side, our page on solar panels in Mitcham has a PVGIS estimate for the town of about 3,983 kWh a year from a 4 kWp south-facing array, and our south-west London solar panels hub covers the boroughs around Merton. DESNZ records about 2,398 solar PV installations of every size across Merton at the end of 2025, as first published.
Sources: UK Power Networks, licence boundaries open data (December 2024), Areas we cover, and Solar and storage: cost, time and what’s involved (read 15 October 2026); NESO GIS boundaries for GB DNO licence areas (May 2024); Ofgem, RIIO-2 Electricity Distribution annual report 2024 to 2025 and supplementary datafile (15 January 2026); Energy Networks Association, EREC G98 Issue 2 (10 March 2025); MCS, Notifying DNOs; ONS Census 2021, TS044 and TS054 for the six Mitcham wards (Nomis, read 14 September 2026); PVGIS 5.3, European Commission Joint Research Centre (PVGIS-SARAH3 2005–2023, run 16 September 2026); DESNZ, Renewable electricity by local authority 2014 to 2025 (29 September 2026).