Why does my home battery drain when Octopus charges my EV?

If you have a home battery, an EV, and an Octopus smart tariff, you may have noticed something frustrating: your battery is depleted during the day when Octopus kicks in to top up your EV outside the overnight window, or your evening battery level is lower than expected on days with daytime EV sessions.

This is not a firmware bug. It is how grid-connected batteries and smart EV chargers interact — and most installers do not explain it at setup time.

What is actually happening

It helps to understand two separate phases.

Phase 1: The off-peak charging window (e.g. 00:30–05:30)

During this window, your battery is charging. A battery cannot charge and discharge at the same time — so while it is filling up from cheap overnight grid power, your home's other loads are also supplied from the grid. Everything — lights, the fridge, any overnight appliances — runs on off-peak electricity while the battery charges. This is working exactly as intended.

Phase 2: After the window ends

Once the off-peak window closes, your battery switches to discharge mode. This is where the conflict happens.

Octopus Intelligent Go does not stop at 05:30. It can schedule additional EV sessions at any point during the day — whenever the grid is clean or cheap — without telling your battery. When a daytime session starts, your EV charger begins drawing power. Your battery sees the household load increase and does what it is configured to do in discharge mode: it supplies that demand.

The result:

• Your battery discharges during a mid-day or afternoon Octopus EV session
• Solar energy you stored that morning is consumed by the car instead of being available for the evening
• Your battery enters the peak-rate evening period with less charge than expected

In an illustrative example, this can add up to a noticeable weekly loss in missed solar storage and unnecessary battery cycling.

Why it happens more with Intelligent Go

Standard Octopus Go charges at a fixed overnight window (typically 00:30–05:30). Your battery charges during that window, and once it ends, the pattern is predictable. There are no unexpected daytime sessions.

Intelligent Go is different. It schedules charging dynamically — sometimes during the day, sometimes in short bursts hours after the overnight window closed. Your battery is in discharge mode and has no way to know a smart charging session is about to start. So it discharges into whatever load appears.

The three most common setups where this bites

Solar + battery + EV on Intelligent Go Octopus dispatches a daytime session. Your battery, which stored solar energy from the morning, discharges to help supply the EV load. You lose solar storage and the cheap rate import benefit is reduced because your own battery is doing the work.

Battery + EV, no solar, on Octopus Go The overnight window ends at 05:30. Your battery starts discharging. A scheduled EV session triggers at 07:00 before the car leaves. Battery cycles unnecessarily when cheap grid power was still available.

Heat pump + battery + EV Your battery is trying to buffer heat pump demand in the morning while also being drawn into EV sessions dispatched later in the day. It never recovers enough charge to cover the evening properly.

What you can do

There are a few approaches, depending on your hardware:

1. Set a battery hold schedule manually Most inverters (Solis, Enphase, GivEnergy) let you set a time window where the battery holds charge and does not discharge into household loads. If you know your Octopus EV sessions happen in a fixed window, you can protect the battery during that window.

The problem: Intelligent Go sessions are dynamic. A manual hold schedule cannot follow them.

2. Use inverter export/import controls Some inverters allow you to set a minimum state-of-charge or disable discharge below a threshold. This reduces (but does not eliminate) battery drain during EV sessions.

3. Use software that detects and responds to EV sessions This is what 1app.energy does. When an Octopus smart charging session is detected, the system has two options depending on conditions:

• Hold mode: the battery is held and everything — home load and EV — runs from the Octopus grid supply during the session. Your battery stays full for the evening.
• Charge mode: the battery is held AND additionally charged during the session, using the same cheap grid supply that is charging your car. This gives you extra stored energy you can use in the evening, sell back on an export tariff, or use to avoid oversizing your battery in future.

The protection follows the actual session, not a fixed schedule. You do not need to configure anything manually.

What this is not

This is not Octopus doing something wrong. The tariff is working correctly — it is finding cheap grid slots and scheduling your EV into them. The conflict is at the hardware integration layer: the battery does not know to hold charge when an EV session starts.

It is also not a problem with your battery or inverter in isolation. Both devices work correctly on their own. The issue is whole-home coordination.

The broader pattern

The EV–battery conflict is the most common version of a wider problem: when multiple smart devices share a home, they can conflict silently. Your heat pump might pull from a battery that was meant to export during peak. Your EV might charge from battery when cheap grid power was available.

These conflicts do not show up as errors. They show up as a battery that is never quite where you expect it to be, and energy bills that are slightly higher than they should be.

If this sounds like your setup, read how 1app.energy solves it — or tell us what devices you have installed and we will review whether your home fits the current rollout wave.