DIY Home Battery Installation Guide UK: Foundations, DNO, Cable Sizing
Installing a home battery yourself is legal in the UK, and it is the one part of a solar setup where the labour saving is genuinely large. But the battery is also the part that can burn your house down if you get it wrong. This guide covers the three things DIY installers actually mess up: where you put it and what it sits on, which DNO form you need, and how to size the cables so they do not melt. If you get those three right, the rest is mostly common sense.
Can You Legally Install a Home Battery Yourself?
Yes, with a clear split between what you can do and what a spark has to sign off. The mechanical work, mounting the battery, building the base, running the cables, is all yours. The final connection to the consumer unit is notifiable work under Part P of the Building Regulations, which means it has to be signed off by a Part P registered electrician, or notified to your local building control before you start. In practice, almost everyone does the heavy lifting themselves and pays an electrician for the final hour of connection and testing.
The other legal requirement is the DNO notification. A battery inverter is a generator as far as your Distribution Network Operator is concerned, even if you set it to zero export, so it needs a G98 or G99 form just like solar panels do. Which one depends on the inverter's AC output rating, not the battery capacity. The full picture on that is further down this page, and the DNO rules are covered in depth in our G98 vs G99 guide.
If you are on the fence about whether the whole thing is worth it, start with our home battery storage guide, which runs the payback numbers, and the battery payback calculator. If you have already decided and want to build the battery itself from salvaged cells, that is a different job, covered in the DIY powerwall build guide. This page is about installing a finished battery properly.
You can install a home battery yourself in the UK, but treat the final electrical connection as a paid-for job. Get the location and base right first, submit the correct DNO form, size the cables for the inverter's full load, and pay a Part P electrician to do the last connection and testing. Skipping any one of those is how batteries end up on the news.
Where to Put It: Foundations and Mounting
Battery placement matters more than most people think, and it is the cheapest mistake to get right. The ideal spot is inside, on a masonry wall or level floor, in a garage or utility room. Stable temperature, no direct sun, no rain, and a short cable run to the consumer unit. Under-stairs cupboards work if there is airflow, but check the manufacturer's clearance requirements before you box a battery in, most want 600mm clear to the front and some airflow around the sides.
Indoor mounting
Wall-mounted batteries go on a masonry wall, never plasterboard alone. Find the studs or fix into blockwork with proper fixings rated for the battery's weight, which on a 5kWh unit is often 50-70kg, plus whatever is stacked on top. Floor-standing batteries sit on a level, non-combustible surface. Keep lithium batteries off escape routes and away from anything flammable, and do not install them in a loft, where summer temperatures wreck the cells and the fire risk is worst.
Outdoor mounting
If the battery must go outside, it needs an IP65 rating and a position out of direct sun, ideally a north-facing wall or under an overhang. For a ground-mounted unit, set it on a level concrete pad at least 100mm thick, or a solid paving slab, raised slightly so standing water drains away. Do not sit a battery directly on soil or grass. And in Scotland or exposed coastal sites, check the manufacturer's minimum operating temperature, many lithium batteries will not charge below 0°C unless they have a built-in heater.
DNO: G98 or G99 for a Battery
This is the bit that catches out first-time battery installers, because the threshold has nothing to do with how much storage you have. The DNO only cares about the inverter's maximum AC output current.
A 5kW hybrid inverter on a single-phase supply is 21.7A at 230V, so it needs G99 even if you never export a single watt. A 3.68kW inverter stays on G98. The rule is the same for batteries as it is for solar, which is why the G98 vs G99 guide is worth a read before you spend any money.
On the hardware side, the inverter-charger most UK DIY battery builds are built around is the Victron MultiPlus-II 48/5000. It is G99-capable, doubles as an AC charger, and its 48V architecture matches the LiFePO4 banks most people build. If you are speccing a system from scratch, this is the default pick.
One more point that trips people up: a battery-only system with no solar still needs the DNO form, because the inverter can export. Setting it to zero export does not exempt you. The DNO does not trust a software setting to stay put forever, and your smart meter will happily record the export if it ever changes.
Cable Sizing: The Part People Undersize
The cable between the battery and the inverter carries DC at high current, and it is where DIY installs go wrong most often. The current is inverter power divided by battery voltage, not the battery's amp-hour rating. A 5kW inverter on a 48V battery draws about 104A at full load. A 10kWh battery and a 20kWh battery both draw the same 104A through the same cable if they feed the same 5kW inverter, because the current is set by the inverter, not the storage.
You size the cable for two things: ampacity (can it carry the current without overheating) and voltage drop (does enough voltage survive the run). For a battery-to-inverter DC run, keep voltage drop under about 1%, because every volt you lose on a 48V system is a bigger percentage than on a 230V AC circuit, and inverters shut down early when the DC bus sags under load.
| Copper cable | Approx. continuous amps | Typical inverter on 48V |
|---|---|---|
| 16mm² | 85A | Up to 3.5kW |
| 25mm² | 110A | 5kW (short runs) |
| 35mm² | 145A | 5-7kW (or 5kW on longer runs) |
| 50mm² | 175A | 8kW |
| 70mm² | 220A | 10-12kW |
Those amp figures are approximate, for double-insulated flexible copper in free air, and they assume a short run. The moment your cable run gets long, voltage drop becomes the limiting factor and you go up a size or two. Worked example: a 5kW inverter on a 48V bank draws 104A. A 25mm² cable rated for 110A is fine for a 1 metre run, but if the battery is 4 metres from the inverter you would drop to 35mm² to hold the voltage loss under 1%. The exact numbers for your setup are what the DC cable calculator is for, use it rather than guessing.
Two rules that apply to every install, whatever the cable size. First, fuse the cable at the battery end, as close to the terminal as physically possible, with a DC-rated fuse or breaker sized to protect the cable. A Class T or MRBF fuse is the standard choice for lithium banks. Second, keep the positive and negative runs the same length and route them together, so the loop is tight and the resistance is balanced. If you are building the battery from cells yourself, the cell-level wiring, busbars and BMS sizing are covered in the BMS buyer's guide and the DIY powerwall build guide.
Common Mistakes to Avoid
Frequently Asked Questions
Can I legally install a home battery myself in the UK?
Yes, with limits. You can do the mechanical work yourself: foundations, mounting, cable runs, racking. The final electrical connection is notifiable work under Part P, so it must be signed off by a Part P registered electrician or notified to building control. The DNO form (G98 or G99) can be submitted by anyone.
Do I need G98 or G99 for a home battery?
Any inverter that can export counts as a generator. G98 covers a maximum AC output of 16A or less per phase (3.68kW single-phase) and is a notification you submit within 28 days of connecting. G99 covers anything larger and needs approval before you connect. This applies even if you set the inverter to zero export.
Where should I install a home battery?
Indoors in a garage, utility room, or under-stairs cupboard is best: stable temperature and a short cable run. If it goes outside, use an IP65 unit on a north-facing wall or under cover, on a level base. Keep lithium batteries off escape routes, away from combustibles, and do not mount on timber surfaces.
What size cable do I need between the battery and inverter?
Size it for the inverter's maximum DC current, which is inverter watts divided by battery voltage. A 5kW inverter on a 48V battery draws about 104A, which needs at least 25mm² copper for a short run or 35mm² for a longer one. Fuse the cable at the battery end and use the DC cable calculator for the exact figure.
Does a DIY battery install affect my home insurance?
It can. A lithium battery without a Part P certificate is a problem if you ever claim. Notify your insurer after installation and keep the electrical certificate and DNO acknowledgment. Some insurers ask about battery storage specifically. Check before you start, not after.
How much do I save installing a battery myself?
The battery itself is the bulk of the cost either way. The saving is in labour: an installer typically charges £1,500 to £3,000 on top of the hardware. Doing the foundations, mounting and cable runs yourself and paying only for the final electrical sign-off typically saves £1,000 to £2,000 on a 5-10kWh system.
What chemistry should a DIY home battery use?
Lithium iron phosphate (LiFePO4) is the sensible choice for a house. It is far less prone to thermal runaway than the older lithium-ion chemistries, lasts thousands of cycles, and is what most reputable home battery brands now sell. Avoid second-hand EV packs unless you genuinely know what you are doing with cell matching and BMS configuration.
Can I wire the battery into my consumer unit myself?
Not in practice. The connection to the consumer unit is notifiable work under Part P, and you need a competent person to sign it off. Do everything up to that point yourself, then pay an electrician for the final connection, testing, and certificate. That keeps the install legal and your insurance intact.
Rather let a professional handle it?
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