The Hardware

What kind of battery cells do you use?

We use Lithium Iron Phosphate (LFP) cells. We chose these because they are incredibly stable and safe, they last a long time, and you can regularly charge them to 100% without the battery wearing out (unlike the batteries in your phone or laptop). They also don't require expensive or scarce metals like Cobalt and Nickel.

What is the capacity?

The battery holds 2.5kWh of energy.

How long does the battery last?

We provide a warranty that covers the battery for 10-years. Over that decade, the cells will slowly lose a small amount of their original capacity, but even beyond that the battery will continue to work and still be useful.

What does the inverter do?

The inverter takes the DC power from the battery and turns it into the AC power your home uses. We use a grid-tie inverter, which means it safely pushes power back into your home through a standard socket.

It is also a critical part of our efficiency. We’ve engineered it to reach a "round trip" efficiency of 90% or more (which is much better than most budget batteries), helping you see a return on your investment much faster.

Using Your Battery

How exactly does it power my appliances?

This is the clever part. When you plug the Windfall Battery into a standard wall socket, it combines with your home's electricity. When the app tells the battery to discharge, it pushes power back into your home’s wiring.

Because electricity follows the path of least resistance, your appliances (like your fridge, TV, or laptop charger) will use the "local" energy from the battery first before pulling any extra power from the National Grid. You don't need to plug your appliances directly into the battery for this to work.

If you turn on a high-energy appliance that exceeds the battery's output (like a 3kW kettle), the grid simply provides the remaining balance. There's no interruption or flickering; the battery just offsets as much of the cost as it can.

During peak times, our software optimises the battery's output to match our estimate of your energy use. This ensures your smart meter sees zero energy flow, so you aren't charged for usage during the most expensive parts of the day.

What happens during a power cut?

The Windfall Battery isn't designed to power your entire house if the grid goes down (mostly for safety reasons). However, it does have a dedicated backup power socket on the front. You can plug your most important device into this, and we’ve included a USB-C port to keep your laptops and phones topped up.

How does it connect to the internet?

The battery uses your home WiFi to get data on energy pricing so it knows the best time to charge. It also uses Bluetooth to make the initial setup with your phone quick and easy.

Can I use more than one battery?

Technically, you could have two, but we are waiting for the UK government to clarify new regulations (specifically from the Department for Energy Security and Net Zero). For now, it’s safest to assume one battery per home.

Does it work with "plug-in" solar panels?

The Windfall Battery doesn’t have a direct port for solar panels, but you can certainly use separate plug-in solar kits in the same home. The two systems would need to "talk" to each other to work perfectly, so we’ll publish a list of compatible solar products once we are closer to shipping.

Is there an API for advanced users?

Yes. If you enjoy tinkering, we will have a free consumer API available to build on. The battery works perfectly out of the box with the Windfall App, but if you want to integrate it into your own custom smart-home setup, then you can.

Will it work with Home Assistant?

While we haven't built a native integration yet, we will support the community in building one using our API.

Savings and the Environment

How exactly does the battery save me money?

It all comes down to "load shifting." The battery moves your energy buying from expensive times to cheap times.

To make this work, you’ll need a "time-of-use" tariff where electricity prices change throughout the day. For example, in the middle of the night when the wind is blowing, but most people are asleep, the price of electricity drops (it can even go negative). The Windfall Battery spots these cheap windows, charges itself up, and then powers your home during the expensive evening peak.

Is it actually better for the planet?

In the UK, the cheapest energy is almost always the cleanest energy. When there is plenty of wind and solar power on the grid, prices drop. By using the Windfall Battery to capture that energy, you are reducing your carbon footprint while saving money at the same time.