wattsworth Get involved
Live pilot · running a real home since September 2026

Your battery, in plain English

Wattsworth is a butler for your home battery. He decides when to charge, when to run the house from it and when to sell back to the grid, so your bill comes down. Ask him anything and he answers in plain words. No kilowatt jargon or settings menus.

Get involved Talk to him

Works with FoxESS batteries and Octopus tariffs today. Runs on our servers, so nothing stops when your phone sleeps.

Give it a go
16:12Ask
Wattsworth
On duty · selling at 4:30pm
Today
Note from Wattsworth
The sun and battery are covering the house. At 4:30pm I'll switch it over to the battery, because grid prices peak at 27p.
Ask Wattsworth…
Plain English, always

Other apps give you settings. He tells you what's happening

Battery apps speak in work modes, SoC targets and kW limits. Wattsworth translates. Every plan, every number and every answer is written so anyone in the house can follow it.

What the inverter is told
workMode: ForceDischarge
window: 16:30 – 19:00
fdPwr: 2500 W · fdSoc: 20%
minSocOnGrid: 20%
agile_out.p_kwh: 23.1
What Wattsworth tells you

“I'll sell about 3 kWh back to the grid between 4:30pm and 7pm while it pays around 23p, keeping about 20% to run the house until the cheap rate starts at 11:30pm.”

Ask, don't configure

“How much have I saved this week?” “When's the cheapest time for the washing?” Type it or say it. He reads the prices, the forecast and his own plan, then answers.

Simple by default

Four tabs: Home, This evening, Ask and My account. There's one story at the top telling you what's happening now and next. You don't need a spreadsheet or a forum thread.

Honest, even on a bad day

Every number he writes has to come from the real data or it's thrown out. If yesterday lost money, he says so plainly.

Calm, considered design

Warm paper, deep green and one pink accent. Clear type, generous space and no flashing gauges. It's an app you'll want to open, not one you have to.

How he works

Three steps, then hand it over

1

Connect

Paste in a FoxESS Cloud key. Wattsworth reads your system's battery size, power limits and history, and sets himself up. There's no new hardware and no Home Assistant.

2

Brief him

Tell him your tariff and the reserve he must never go below. Start in simulation if you like. He shows you exactly what he would do without touching the battery.

3

Leave it with him

Every 30 minutes he re-plans the next day and only sends a change to the battery when it matters. Take back control any time with one tap.

Half-hourly prices, in and out Solar forecast for both roof faces How your house actually uses power Battery charge, right now Battery wear, priced in
Real savings · one real home

The numbers, straight from the house

These aren't modelled examples. They come from the pilot home: a FoxESS battery, solar on two roof faces, Octopus Economy 7 for import and Agile Outgoing for export. Figures are as of 2 October 2026.

Savings
Net saving
+£7.37
From Wattsworth
+£1.36
Worth about a pint at the pub.
Powered your home+£11.25
Sold to the grid+£1.23
Charging it used−£5.11
£5.72 spent · 62p still stored

28 Sept – 2 Oct · 5 days · screenshot from the live app

Since pricing went live · 12 Sept – 1 Oct
From Wattsworth, after wear
+£4.07
Before battery wear
+£7.48
Net saving is what the battery and Wattsworth saved together, compared with having no battery at all.

From Wattsworth is the part he added on top of the battery's own built-in mode, after charging 7p for every extra kWh of battery wear. That's the stricter number, and it's the one we quote.

The first three weeks were a working shakedown. Fixes included a wrong tariff, a solar forecast that only saw half the roof and a load forecast running 27% low. Recent days are cleaner than the totals suggest.

Estimated yearly savings

Where it is now, and where it's heading

Battery + Wattsworth, today's pace
~£540/yr

This week's +£7.37 over five days, carried across a year. That's autumn, on one house.

Wattsworth's share, today's pace
~£100/yr

On top of the battery's own mode, after wear. This is the pilot's current run-rate.

Wattsworth's share, potential
£175–260/yr

What's realistic as forecasts settle: half to three-quarters of the best possible plan.

All estimates are compared with the battery's own self-use mode on this home's tariff. They come from a backtest of real September days. Winter shifts the balance towards overnight charging, and EV and heat-pump control (see below) would add to this.

Inside the app

Built from a design system, not a dashboard

Every screen uses the same small set of parts. These are pulled straight from the Wattsworth design system and chat design. The cards hold example content; the savings above are real.

HomeThe story at the top
10:26 · Europe/London
Good morning
Right now the sun and battery are covering the house until 4:30pm. Then I'll switch it to the battery, because grid prices are at their peak.
Ask me more →
AskBest window · dishwasher
Best window · dishwasher · 2h
12:30 – 14:30
Right on your solar peak, so it should run almost entirely on sunshine.
0006121824
AskHe proposes, you decide
Proposed change
Raise tonight's target to 100%, 11:30pm – 6:30am.
Adds 4.6 kWh at 10p, about 46p. Tonight only.
ApproveLeave it
Concept · coming with chat control
HomeThe battery, now
The battery, now
82%
6.2 kWh in hand ·
6 hours of the house
Your floor, 20%10.0 kWh
This eveningThe arrangements
The plan
What I'll do
Overnight · 11:30pm to 6:30am at 10p
I'll top up to about 70%. Tomorrow's sun should cover the rest.
Tomorrow
About 18 kWh of sun is forecast, and the house usually uses about 17 kWh.
Ask“Why did it charge at 2am?”
Night rate was 10p and tomorrow's forecast was grey, so I filled to 90% while it was cheap rather than buying at 27p in the afternoon.
Bought overnight5.8 kWh · 58p
Would have cost by day£1.57
The story so far

From an idea to a working butler in a month

Wattsworth started with one frustration. A home battery that's set once in an app and left alone quietly leaves money on the table every day, and nobody can explain why.

  1. 8 September 2026

    The idea

    Research into FoxESS's API, Octopus tariffs and competing apps. The plain-English product description was written before any code.

  2. 9 September

    First code

    Foundations and integrations: FoxESS Cloud, Octopus prices and Solcast solar forecasts.

  3. 12 – 17 September

    Simulation

    The planner ran every half hour against real prices without touching the battery.

  4. 18 – 22 September

    Live control

    The first real commands went to the inverter, with a safety watchdog, write limits and one-tap “Take back control”. It has run continuously since the 22nd.

  5. 27 – 28 September

    He learns to talk

    The Ask chat and the plain-English Home story arrived. Real tariffs and both roof faces were wired in.

  6. 1 October

    Honest accounts

    Savings are now shown after battery wear, so the number we quote is the cautious one.

  7. Now

    Proving it with real data

    A month of daily tuning on one real home. The aim is to be demonstrably good before opening it up.

Current status · October 2026
  • Live and in full control of one pilot home, around the clock
  • FoxESS KH-series inverters today. Other FoxESS models are next.
  • Any Octopus time-of-use tariff, plus Agile Outgoing export
  • Plain-English Ask chat (text and voice) that explains everything and changes nothing yet
  • Not yet open to the public. Join below to hear first or help test.
What's next

One butler for the whole house

The battery is where he starts. Next come the other big, flexible loads in the house, all planned together and explained the same way.

Get involved

Ring the bell, we'll be in touch

Wattsworth is still a pilot. Leave your name and email if you'd like to follow along, help test it on your own battery, or talk about building it with us. We'll only write when there's something worth saying.

Note from Wattsworth
I'll keep your details discreetly. No sharing, and I'll delete them whenever you ask.
Questions

Before you ring the bell

Can I use it today?+

Not yet. Wattsworth runs one pilot home while we prove the savings with real data. Join the list and you'll hear first when testers are needed.

Do I need Home Assistant or new hardware?+

No. Wattsworth talks to your inverter through the FoxESS Cloud API using a key you generate in about two minutes. There's nothing to wire and nothing to plug in.

Does the AI chat control my battery?+

No. The planner controls the battery, inside hard safety limits. The chat explains what it's doing and answers questions, and it can't change anything. Changing things by asking is planned, and it will always need your approval.

Which systems does it work with?+

Today it works with FoxESS KH-series hybrids on Octopus time-of-use tariffs, with Agile Outgoing export. Other FoxESS models come next, then other brands.

Will all the cycling wear my battery out?+

Wear is priced into every plan, at 7p for each kWh cycled, so he only moves energy when the saving beats the cost. The savings figures we quote already subtract it.

What data do you keep?+

Only what a plan needs: your tariff, your battery's live state and a learned picture of how the house uses power. It's never sold or shared, and it's deleted on request.