Home battery storage: 10 things to know before buying

Helpful video reference. We use the Artisan Electrics video "10 Things You Need To Know Before Getting Home Battery Storage Installed" as the reference here. Artisan Electrics is a Cambridge-based electrical company specialising in renewables and EV charging, with over 300,000 YouTube subscribers. Their team covers the buying decision from a practitioner's perspective - capacity, warranty, siting, and the questions that separate a good quote from a bad one. Worth watching before you take the first call from a sales rep.

1. Understand capacity vs usable capacity

The number on the box - 10 kWh, 13.5 kWh, 16 kWh - is the nominal capacity. It is not the usable energy you actually get. Most lithium batteries are designed to operate between about 10% and 90% of their total capacity to protect the cells and extend their working life. That means a 10 kWh battery typically delivers around 8 to 9 kWh in real use.

Ask each installer what the usable capacity is, not just the nominal figure. Some manufacturers are good about publishing this clearly. Others bury it in the data sheet. The usable figure is what matters for payback calculations.

2. Decide whether you need solar panels first

A battery without solar panels is not pointless. If you are on a smart time-of-use tariff, you can charge the battery overnight at a lower rate (often 7-10p per kWh) and discharge it during peak hours (often 30-40p per kWh), banking the difference. Whether that arbitrage pays back the cost of the battery depends on the spread and how consistently you can manage it.

With solar panels, the battery captures the surplus daytime generation you would otherwise export at the Smart Export Guarantee rate (typically 4-15p per kWh depending on your deal). Instead of exporting at a low rate, you store that energy and use it in the evening at full import price. The more surplus you generate and would otherwise export, the better the case for adding a battery.

If you have solar already, check your generation data to see how much you export. If you already use most of your generation, a battery may add less than you expect.

3. Know the difference between AC-coupled and DC-coupled

This is the question most salespeople skip, but it affects efficiency and cost.

• DC-coupled: The battery connects to the solar array on the DC side, before the solar inverter. A hybrid inverter handles both solar and battery. More efficient because energy is only converted once (DC to AC). Best for new solar-plus-battery installs where you are starting from scratch.
• AC-coupled: The battery has its own inverter (a battery inverter or bidirectional inverter). It connects on the AC side. Easier to add to an existing solar system without replacing the original inverter. Slightly less efficient because energy is converted twice - DC to AC by the solar inverter, then AC to DC by the battery charger, then DC to AC again on discharge.

For retrofit to existing solar, AC-coupled is usually the simpler and cheaper option. For new installs, DC-coupled hybrid systems are worth pricing up.

4. Insist on an MCS-certified installer

MCS (Microgeneration Certification Scheme) is the industry standard for small-scale renewables and battery storage in the UK. An MCS-certified battery installer has demonstrated they follow PAS 63100, the code of practice for the safe installation of electrical energy storage systems in homes.

Why does this matter practically? Without MCS, you are not eligible for Smart Export Guarantee payments for any associated solar generation - payments for the electricity you export to the grid. The installer should be able to show you their current MCS certificate on request. If they are vague about certification, that is a reason to move on.

5. Check the DNO notification requirement

Your distribution network operator (DNO) needs to know about battery storage connected to the grid. The route depends on the size of the inverter:

• G98: Applies to single-phase inverters up to 3.68 kW. The installer notifies the DNO after installation - no prior approval needed. Most home battery systems fall into this category.
• G99: Applies to larger systems. The installer must get DNO approval before connecting the system to the grid. This can add weeks to the project timeline.

Your installer handles the paperwork. But if you are on a tight timeline, ask upfront which route applies to the system they are proposing.

6. Plan where the battery will go

Batteries have physical requirements that often get overlooked until the installation day:

• Temperature: Most lithium battery systems operate between 0°C and 40°C. An unheated UK garage should be fine in most winters, but a particularly cold snap can cause the battery management system to limit charging. Avoid locations that drop below freezing regularly.
• Ventilation: Lithium batteries are safer than older chemistries but they still require adequate ventilation. Do not install in a sealed room with no airflow.
• IP rating: Many batteries are rated IP55 - suitable for a dusty or damp garage but not for rain exposure. They are not outdoor units unless specifically designed as such.
• Proximity: The battery needs to be within reasonable cable distance of the consumer unit and the solar inverter. Every extra metre of DC cable adds cost and small losses.

7. Read the warranty terms carefully

Battery warranties come in two parts and manufacturers are not always straightforward about the difference:

• Product warranty: Covers defects and failure. Typically 10 years for reputable brands.
• Capacity retention guarantee: The manufacturer guarantees the battery will retain a minimum percentage of its original capacity after a certain number of cycles or years. A common figure is 70% capacity after 6,000 cycles or 10 years.

Ask whether the warranty is transferable if you sell the house. Ask what happens if the manufacturer exits the UK market - warranties backed by a parent company are stronger than those backed by a UK sales subsidiary alone. And check whether the labour warranty matches the product warranty or falls short.

8. Check smart tariff compatibility

A battery that cannot be told when to charge and when to discharge is leaving money on the table. Most modern battery management systems can be set on a timer, but some also integrate directly with smart tariff platforms.

If you intend to use a time-of-use tariff - Octopus Flux, for example, which charges different rates for different periods of the day - check that the battery's software can accept the tariff schedule and act on it automatically. Some combinations work out of the box. Others require a third-party energy management system or a manual schedule. Ask the installer to demo how the scheduling works before you commit.

9. Confirm the VAT rate applies correctly

Standalone home battery storage has been zero-rated for VAT since 1 February 2024. Solar panels and batteries installed together have been zero-rated since April 2022. This means a compliant domestic installation should not attract 20% VAT.

If a quote shows 20% VAT on a domestic battery storage installation after these dates, ask the installer to explain. It may be a commercial installation, an error, or the installer is not applying the exemption correctly.

10. Get three quotes and ask the right questions

Price varies considerably for battery storage. Three quotes gives you a range and a basis for comparison. When you have each installer on site, ask:

• Are you MCS-certified for battery storage? (Ask to see the certificate.)
• Will this installation comply with PAS 63100?
• Will I receive an Electrical Installation Certificate?
• What battery brand are you proposing, and why that one?
• What is the usable capacity, not the nominal?
• What is the cycle life and capacity retention guarantee?
• What is your estimate of the payback period based on my usage?
• What DNO notification applies?

Any installer who cannot answer these questions clearly, or who is impatient about being asked, is probably not the right choice for a system you expect to last ten or more years.

When to call us

Richard works alongside MCS-certified solar and battery partners covering east Kent. If you want independent electrical advice before committing to a battery installation - or if you need the consumer unit prepared for a new system - call or message with what you are planning.