Battery Storage FAQ

No. A battery pays back two ways. With solar, it captures surplus you'd otherwise export at 5-15p and lets you use it at 28-30p later, lifting self-consumption from around 40% to 70-80%. Without solar, it charges from a smart time-of-use tariff in a cheap overnight window and runs your home through the evening peak. Both work. The right answer depends on your tariff and when you actually use electricity. See our battery worth-it guide for the full maths.

Any tariff with a meaningful gap between off-peak and peak rates. In our 2026 Big 6 comparison, off-peak import runs from around 7p on overnight EV tariffs to about 13-16p on battery-focused plans such as Octopus Cosy and Flux. Peak import typically sits around 25-30p. Ofgem maintains a neutral overview of smart and time-of-use tariffs. The differential matters more than the supplier name. We size your battery against your chosen tariff so the daily cycle pays back.

It depends on the system. By default, batteries disconnect when the grid drops under G98/G99 anti-islanding rules, so Fox ESS systems shut down in a power cut. Tesla Powerwall 3 installs include the Backup Gateway 2, which switches your consumer unit to battery power and keeps the whole home running through an outage. If outage cover matters to you, Powerwall 3 is the one to pick.

For most retrofits, AC coupling. An AC-coupled battery sits alongside your existing inverter and charges from spare power on your house circuit, leaving panels and inverter unchanged. DC coupling uses a hybrid inverter for roughly 5% better efficiency but means replacing the inverter. We default to AC on retrofits unless your inverter is end of life or the efficiency gain pays for the swap. We confirm during the quote.

Most UK 3-bed homes suit a 10 kWh battery. With an EV, you usually charge the car from the off-peak tariff overnight rather than the battery, since both use the same cheap window. A 10-13 kWh battery covers household use. With a heat pump, we often size 13-20 kWh to bank cheap-rate power for evening heating peaks, often paired with Cosy or similar. Sizing happens at quote stage.

We notify your Distribution Network Operator (DNO) that the battery is being installed. For most domestic batteries on a single-phase supply, this is a G98 notification, which is a post-install notification. Larger systems above the G98 threshold need a G99 application before the install, and the DNO has up to 65 working days to respond. Battery-only is usually simpler than solar+battery because there's no generation export application required. We handle all the paperwork.

Yes. The battery and inverter you install today work with panels added later. Tesla Powerwall 3 has a built-in solar inverter; Fox ESS uses an H1 hybrid inverter ready for solar input. At add-on time you pay for panels, mounting, and MCS paperwork for the Smart Export Guarantee. Mention solar plans before install so we size the inverter correctly.

No. The Powerwall 3 has a hybrid inverter built in, with three MPPT trackers and support for up to 20 kW of solar input, so it runs solar panels directly with no separate inverter box on the wall. That also makes it a tidy choice when an existing solar inverter is nearing end of life: the Powerwall replaces it and adds 13.5 kWh of storage in one unit.

A Fox ESS H1 single-phase hybrid inverter, sized at 3.7, 5.0 or 6.0 kW to suit your setup, with up to a 10-year warranty. It manages the battery and any solar panels together, and pairs with Fox ESS EP6 (5.76 kWh) and EP12 (11.52 kWh) battery modules. For AC-coupled retrofits alongside an existing solar inverter, we confirm the right configuration as part of your fixed online quote.

Modern lithium iron phosphate (LFP) batteries are rated for around 6,000 charge cycles, which works out to roughly a decade of cycling once a day. The standard manufacturer warranty is 10 years and guarantees the battery will hold at least 70-80% of its original capacity at the end of that period. After the warranty most batteries continue running with reduced capacity rather than failing outright. UKEM adds a 2-year workmanship warranty on top of the manufacturer cover.

Yes, for short periods. A 10 kWh battery covers typical evening use for around 6-12 hours, less with heavy draws like an oven, immersion heater, or EV charging. Whole-home backup during an outage needs a Tesla Powerwall 3, which comes with the Backup Gateway 2 and supports 11 kW output. Most homes use batteries to cut bills, not live off-grid full time.

Standalone home battery installs typically run from around £4,000 (Fox ESS EP6 at 5.76 kWh) up to £12,000+ (Tesla Powerwall 3 at 13.5 kWh with whole-home backup). The price covers the battery, hybrid inverter where required, isolators, wiring, commissioning, MCS paperwork and DNO notification. A retrofit to existing solar takes around a day. Get a fixed, personalised price through our online quote tool.

No. Battery storage is currently zero-rated for VAT under the energy-saving materials relief. The relief is set to end in March 2027, after which VAT is expected to return to the previous 5% reduced rate. On a £6,000 battery that's still a £300 difference, so installing before the deadline locks in the bigger saving. The relief is automatic, you don't need to apply for it.

Not on its own. The Smart Export Guarantee (SEG) pays for surplus electricity you export, and a standalone battery generates nothing to export. With solar, a battery actually reduces SEG income, because more of your generation gets used at home instead of sold back. That trade is usually in your favour, since the import savings are 3-5x larger than the export rate. See the Ofgem SEG page for current rates.

Most battery-only installs take around a day on site. No scaffolding, no roof access, no DNO solar generation application. The engineer mounts the battery (typically in a utility room, garage, or outside), wires it into your consumer unit through an isolator, commissions the system, and walks you through the app. Quote to install is usually 3-5 days for a standard retrofit. Powerwall 3 installs add around half a day for the included Backup Gateway and circuit reconfiguration.

The most common locations are utility rooms, garages, and outside walls. Batteries are wall-mounted and need a flat, structurally sound surface plus enough clearance for ventilation. Indoor installs need a frost-free room (most batteries derate below 5°C). Outdoor installs use IP65-rated units and are usually mounted in a sheltered spot. We confirm placement during the quote based on cable runs to your consumer unit and where you have suitable wall space.

Yes. Selected home batteries qualify for 0% interest finance over 12 to 24 months with no deposit, or longer terms up to 15 years from 9.9%APR Representative, subject to status. The Tesla Powerwall 3 27 kWh option is available on the pay-monthly plan only, not at 0%. Finance is through FCA-authorised lenders; UKEM Group is an Appointed Representative of Shermin Finance Limited. Many households align repayments with time-of-use tariff savings. See our finance page for how options are structured.

No for a quote alone; yes if you apply for finance. Getting an installation price doesn't touch your credit file. A full finance application runs a credit check recorded on your file, and only happens once you choose regulated credit. See our finance page for details.

Roughly a full day of normal use. Ofgem's typical UK household uses about 7.5 kWh of electricity a day, so a 10kWh battery covers an evening peak, overnight and the next morning, while a 5kWh unit covers a typical evening. High-draw appliances shorten that: an electric shower or oven pulls 2-3 kWh in a single use. Heat pumps and EV charging need their own sizing maths.

No, not in most cases. Home batteries are normally installed under permitted development rights in England, Wales and Scotland, whether wall-mounted or floor-standing. The exceptions worth checking: listed buildings, conservation areas, and flats. Your installer handles the paperwork that does apply, the DNO (network operator) notification, as part of the job.

The main disadvantages are upfront cost, storage losses, gradual capacity fade and the space the unit takes up. Payback depends on the gap between your import rate and what you'd otherwise export or buy off-peak. Round-trip losses mean you get back roughly 90% of what you store. Capacity fades to around 70-80% by the end of a typical 10-year warranty. And a battery needs wall or floor space in a garage, utility room or outside.