Backup power with a home battery: what works and what doesn't
Last updated: 30 September 2026 · By Team Multi-Solar, home batteries since 2022, Rotterdam
A regular home battery does not supply power to your home during a power cut: just like the inverter of your solar panels, it disconnects from the grid. You only have backup power if the battery has a separate backup power output, or if an installer fits a changeover switch in your electrical panel. With a plug-in home battery, this keeps the appliances running that you connect to that output. With a fixed battery and a changeover switch, the whole house can keep running. Below you can read about the three levels, how long you have power and what doesn't work.
Why does a battery normally switch off during an outage?
A battery or inverter connected to the grid may not simply send power onto the grid during an outage. Otherwise a cable that a technician is working on could suddenly be live again. That is why inverters and batteries automatically disconnect as soon as the grid fails or the voltage is not right. If you still want power in your home, your home has to be physically separated from the grid before the battery starts supplying power. That is done by a backup power output on the device itself, or by a changeover switch in the electrical panel. Feeding power back into the electrical panel yourself is dangerous and not permitted; always have this done by a certified installer.
What are the three levels of backup power?
| Level | What keeps working | What you need | Who connects it |
|---|---|---|---|
| 1. Backup power output | Only the appliances you connect to the battery's output | A plug-in home battery with backup power output | You yourself |
| 2. Critical circuits | Selected circuits, for example fridge, lighting, router, central heating boiler | A backup box or changeover switch with separate backup power circuits | A certified installer |
| 3. Whole house | Everything within the power of the system | A fixed battery with changeover switch | A certified installer |
In the Netherlands, we arrange levels 2 and 3 via a quote, because every electrical panel is different.
Level 1: how does the backup power output of a plug-in home battery work?
Many plug-in home batteries have a separate socket for backup power in addition to the grid connection. You switch on the backup function in the app; if the grid fails, that socket supplies power from the battery. Anything you don't connect to it stays without power.
| Battery | Backup power output |
|---|---|
| Marstek Venus A | 1,200 W |
| Marstek Venus E Mini | 1.5 kW |
| Marstek Venus E 3.0 | 2,500 W |
| Marstek Venus E 4.0 | 3,000 W, briefly up to 3,600 W, switchover within 10 ms |
| Marstek Venus Max | 3,600 W, switchover within 10 ms |
In practice, you use an extension cable or power strip to connect what you really need: fridge or freezer, router, a few lamps, phone chargers, possibly the laptop. Add up the power of what you connect; the rating plate or the manual of the appliance states it. A kettle or hair dryer quickly draws 2,000 W and then takes up almost everything a Venus E 3.0 can deliver.
The limitation is clear: the rest of the house stays dark, and circuits in the electrical panel are not taken over automatically.
Level 2: how do you get critical circuits on backup power?
Here an installer creates a separate backup power distribution board with the circuits that must keep working during an outage. A backup box or changeover switch detects that the grid has failed, disconnects those circuits from the grid and switches them to the battery. You decide in advance which circuits you choose. Often these are:
- the circuit with the fridge and freezer;
- the lighting in the living room and kitchen;
- router and modem;
- the central heating boiler and its pump;
- possibly a workstation or medical equipment, in consultation with the installer.
Such boxes exist per brand. AlphaESS has the BB Plus Backup Box, which according to the manufacturer switches over within 10 ms. A Smart Backup Box has been announced for Marstek plug-in home batteries, but according to Marstek it is still in development at the moment. Ask us about the current status if you want this for a Marstek battery.
Level 3: how do you keep the whole house running?
For backup power throughout the whole house, you need a fixed battery with a changeover switch that separates your complete installation from the grid.
- The Marstek Venus X supplies 6 kW continuously and up to 12 kW peak, and switches over within 10 ms. It is single-phase, expandable to 60 kWh, and the installer fits the changeover switch. Because solar panels up to 7.5 kW run through the Venus X, they can keep supplying power during an outage and recharge the battery.
- With Enphase, the IQ System Controller 3 INT switches over automatically and forms its own microgrid, in which the IQ Battery and the solar panels keep supplying power. It can be set to single-phase or three-phase.
- With Sigenergy, the Sigen Energy Gateway HomePro does the same, in single-phase or three-phase, with switchover in 0 ms.
- AlphaESS combines the Smile G3 with the BB Plus Backup Box.
If you have a three-phase connection, the backup power system must match it. What that means is explained in single-phase or three-phase. You can see all systems under fixed home batteries, and per brand under AlphaESS and Enphase.
How long do you have power? Here's how to calculate it
- Usable capacity: the capacity in kWh multiplied by the depth of discharge. According to the brochure, the Venus E 4.0 uses 88 percent of its cells.
- Power of what you connect: add up the power ratings in kW.
- Divide one by the other: usable kWh divided by kW is the number of hours.
An example: suppose the fridge, router and a few lamps together draw an average of 0.25 kW, and you have 5 kWh usable. Then you have about 20 hours of power. With the central heating boiler and a TV added, that becomes shorter. This is a worked example, not a promise: a fridge switches on and off, and you can see your actual consumption in the app.
Important: the battery does need to be charged at the moment the outage occurs. With most brands, you can set a reserve in the app so that the battery never runs completely empty through daily use. Which capacity you need is explained in how many kWh of home battery you need.
What doesn't work, or not just like that?
- Heat pump, induction hob, oven and washing machine on a plug-in home battery. These require more power than a backup power output supplies, or start with a peak that makes it switch off.
- Solar panels on a regular inverter. These switch off during an outage and therefore supply no power, not even to your battery. Only a system that separates your home from the grid, such as the Venus X or an Enphase microgrid, keeps them working.
- Three-phase appliances on a single-phase battery. A three-phase hob or charging point does not run on single-phase backup power.
- Feeding backup power back into the electrical panel yourself. Life-threatening for technicians and not permitted. Only via a changeover switch fitted by an installer.
- An empty battery. Without a reserve set, the battery may just be empty when the outage starts.
Frequently asked questions
Does a home battery work during a power cut?
Only if it has a backup power output, or if there is a changeover switch in the electrical panel. A battery without those functions switches off during an outage, just like the inverter of solar panels.
How long can a home battery supply backup power?
Divide the usable capacity in kWh by the power of what you connect in kW. With 5 kWh and 0.25 kW of fridge, router and lighting, that is about 20 hours, provided the battery was full.
Do solar panels work during a power cut?
Not with a regular inverter: it switches off. They only keep supplying power in a system that separates your home from the grid and creates its own power network, such as the Venus X or an Enphase system with System Controller.
Which appliances can I connect to backup power?
Anything whose combined power stays below the maximum of the output: fridge, router, lighting, chargers, laptop. Check the rating plate. It is better not to connect appliances with large peaks, such as a kettle or oven.
Can a heat pump run on a home battery during a power cut?
Not on a plug-in home battery. With a fixed battery with sufficient power and a changeover switch for the whole house, sometimes it can, depending on the power and the number of phases. An installer assesses this in the quote.
Want backup power for a few appliances? View the plug & play home batteries with backup power output. Want to keep the whole house running? Request a quote for a fixed battery with changeover switch. The complete range can be found under home batteries; the difference between the two routes is explained in plug-in or fixed.
Sources
- Marstek Nederland, "Hoe zet je de back-upfunctie aan in de Marstek-app voor de Venus E?" (31 January 2026): backup socket up to 2,500 W, Smart Backup Box still in development
- Marstek, brochure Venus E 4.0: off-grid 3 kVA, peak 3.6 kVA for 10 s, depth of discharge 88 percent
- Enexis (Dutch grid operator), "Mijn omvormer valt uit" (consulted 30 September 2026)
- Product data Marstek, AlphaESS, Enphase and Sigenergy: manufacturer documentation and product pages multi-solar.nl (30 September 2026)