Off-Grid · Power · Batteries
Batteries: The Heart of the System
The panels get the glory, but the battery is what actually runs your house — it's the difference between "free power while the sun's up" and "a home." It's also the one place not to save money, because the wrong battery is a false economy you pay for twice. Get this choice right and it quietly cycles for a decade; get it wrong and you're back at the shops in two winters.
Your solar array fills the battery through the day; the battery runs the lights, the fridge, the pump and the laptop through the evening and night. Size and choose it well and it's the most important spend in the whole system.
Buy LFP (lithium-iron-phosphate). This is the one clear answer. For a home off-grid bank in 2026, LiFePO₄ is the right chemistry — safe, long-lived, and happy to be deep-cycled every single day. Cheap lead-acid looks tempting on the shelf and dies young the moment you actually use it hard. Over ten years the lithium is cheaper andbetter. Don't agonise over this bit.
How the battery fits with the array, the inverter and the generator — the whole system.
Read the hub →☀️ Solar panelsWhere the charge comes from — ground-mount, sizing and winter tilt.
Read the guide →🔌 Inverter/chargerThe box that turns this battery's DC into the 230 V that runs the house.
Read the guide →The chemistries, honestly LFP wins
LFP / LiFePO₄ — the off-grid standard
Thousands of deep cycles (often 4,000–6,000+), you can safely use ~80–90% of the rated capacity, it holds voltage well, and the chemistry is the safest lithium type — it won't run away like the laptop-style NMC cells. It costs more up front and it's worth every penny. This is what to buy.
Lead-acid — the classic false economy
Cheap to buy, miserable to live with. To get any life out of it you can only use about half its capacity, it hates being left partly charged (exactly what off-grid does in winter), and it wears out in a few hundred cycles. You buy it twice or three times while the LFP is still going strong. Skip it.
NMC / other lithium — leave it to the car people
Higher energy density, but less tolerant of abuse and less safe for a DIY home bank. There's no reason to choose it over LFP for a stationary house battery. LFP is the grown-up choice for living with.
How much battery do you need? size it honestly
Start from your real daily use
Add up what you actually run in a day — lights, fridge (the biggest steady load), laptop, phone charging, water pump, a bit of telly — in watt-hours. That daily number, times how many grey days you want to ride out without the generator, is your usable capacity. Most simple off-grid homes land somewhere around a few kWh of usable LFP; add more if you want longer autonomy through winter.
Autonomy is the winter insurance
"Days of autonomy" is how long the battery alone carries you with no sun. One day is tight; two to three is comfortable and means the generator only comes out in a genuinely black spell. More battery buys quieter winters — it's the trade-off against generator fuel and noise.
48 volts, a BMS, and how to buy it
Build the house bank at 48 V
Small setups run at 12 V; a whole house is far better at 48 V — thinner cabling, less loss, and it's what serious inverter/chargers and controllers expect. If you're powering a home rather than a campervan, start at 48 V and save yourself a rebuild.
Prebuilt server-rack packs vs a DIY build
Two sensible routes. Prebuilt 48 V server-rack LFP modules come with a built-in BMS, stack neatly, and are close to plug-and-play — the easy, reliable choice. Or build your own from cells plus a separate BMS: cheaper per kWh and satisfying if you're handy, but you must do the balancing and safety properly. Either way, a good BMS (battery management system) is non-negotiable — it's what protects the cells and, crucially, stops charging when it's freezing.
Cold winters change the rules read this
Never charge LFP below freezing
Here's the one that catches people in an upland French winter: LFP must not be charged below 0 °C — do it and you permanently damage the cells. Discharging cold is fine; charging cold is not. A decent BMS blocks it automatically, but the real fix is to keep the bank somewhere it never freezes.
Keep the bank in the warm room
Site the battery inside your insulated, wood-heated one warm room, not in a stone barn that hits −5 °C. It'll hold more capacity, charge freely, and last longer. A cold battery is a smaller, unhappier battery — keeping it warm is free performance.
What it costs — and the real economics
DIY ranges for the bank only. The honest comparison is cost over its life, not on the shelf.
- £500–1kA small LFP bank (a kWh or two usable) — enough for a simple off-grid life: lights, fridge, laptop, charging.
- £1.5–4kA comfortable household bank (several kWh usable, 48 V), with a couple of days' winter autonomy.
- the catchLead-acid that looks half the price up front costs more over ten years once you've replaced it two or three times. Buy the LFP once.
Could wind help fill the bank?
On an exposed plot a small turbine tops up the battery through the dark, still weeks when the panels fall short. See where it does and doesn't pay.
Wind turbines, honestly →