Pairing a home battery with a generator is now built into several major backup systems. FranklinWH’s aGate can start and stop a generator automatically through an optional module. Enphase’s IQ System Controller 3G adds a dedicated generator port, which Enphase says works with most AC generators installed in the US. EcoFlow’s Smart Home Panel 2 manual lists support for 120V or 240V generators from 3 to 12kW. Generac’s PWRcell 2 Smart Disconnect Switch supports Generac standby generators up to 28kW. The idea is simple: the battery handles the quiet hours, and the generator runs only to refill it. This guide explains the pairing options, how to size the generator and what a day of runtime looks like.
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Product details come from FranklinWH, Enphase, EcoFlow and Generac documentation, as covered in my earlier reviews and linked below. Runtime and fuel figures are my estimates.
Why pair a battery with a generator?
In my generator vs battery backup guide, the deciding factor was outage length. A battery is silent, instant and fuel-free, but it runs out. A generator runs as long as you have fuel, but it’s loud, needs maintenance and burns fuel even at light loads. Together, each covers the other’s weak spot:
- Battery first: the home runs silently from the battery, with no gap when the grid drops.
- Generator on demand: when the battery gets low, the generator starts, carries the house and recharges the battery at an efficient, heavy load.
- Generator off: once the battery is full, the generator shuts down, often for most of the day.
A generator running only a few hours a day uses far less fuel than one running around the clock at a light load, so a tank of propane or a few gas cans can last much longer.
Three ways to pair them
| Approach | Examples | Generator control | Best for |
|---|---|---|---|
| Integrated home battery system | FranklinWH aGate, Enphase IQ System Controller 3G, Generac PWRcell 2 with Smart Disconnect Switch | Automatic start/stop from the battery system | Whole-home backup with a hardwired standby generator |
| Portable home battery with a smart panel | EcoFlow DELTA Pro Ultra with Smart Home Panel 2 | Generator settings in the app; manual interlock between grid and generator | Homes that want backup without a permanent battery wall |
| Portable power station charged by a portable generator | A 2kWh power station plugged into a 120V inverter generator | Manual | Essentials-only backup: fridge, internet, lights, CPAP |
Option 1: integrated systems
FranklinWH aPower 2 + aGate
The aGate is FranklinWH’s smart switch for managing grid, solar, battery and generator. With the optional generator module, it can start and stop a standby or portable 240V generator automatically, run the home from it and recharge the batteries. FranklinWH recommends about 12kW of generator for one aPower 2 and about 23kW for two, and it supports one generator source at a time. More in my FranklinWH aPower 2 review.
Enphase with IQ System Controller 3G
Enphase’s third-generation system offers two controllers. The IQ System Controller 3G has a dedicated DER port for a generator, which can’t be used for PV or batteries. Enphase says no external automatic transfer switch is needed, and the Enphase App can remotely start and stop the generator, schedule quiet time and turn on a vacation mode. Enphase’s planning advice is clear: if you might add a generator later, choose the 3G. If you’re more likely to add batteries, choose the standard IQ System Controller 3. My Enphase IQ Battery 5P review covers the battery side.
Generac PWRcell 2
If you already own a Generac standby generator, PWRcell 2’s Smart Disconnect Switch is designed to integrate it, supporting Generac generators up to 28kW. I compared it with Tesla’s system in Generac PWRcell 2 vs Powerwall 3.
Option 2: EcoFlow DELTA Pro Ultra + Smart Home Panel 2
EcoFlow’s Smart Home Panel 2 connects DELTA Pro Ultra batteries to your home circuits and can also take a generator through an inlet box. According to EcoFlow’s manual, you set the generator type (120V single-phase or 240V split-phase), the maximum generator power (3–12kW) and how much of that power goes to charging the batteries, since the generator may be feeding home loads at the same time. Switching between grid and generator is done with a physical interlock on the panel, not in the app.
EcoFlow’s manual has two more details worth knowing. After you connect the generator and switch it on, it takes about 25 seconds for the house to get power. And if your generator has a bonded neutral, EcoFlow says the bond should be removed by an electrician before connecting, or the panel’s GFCI/AFCI protection won’t work properly. My DELTA Pro Ultra review covers capacity and scaling.
Option 3: a power station and a portable generator
This is the simplest and cheapest pairing. Run your essentials from a 2kWh-class power station all night, then plug the station’s AC charging cable into a 120V inverter generator in the morning. The generator only has to run for an hour or two, at a strong, efficient load. My Delta 3 Max generator charging guide shows how to match the station’s charge rate to your generator’s real output, and the same logic applies to any brand. Use a pure sine wave inverter generator. Many power stations also have a setting for unstable AC input that helps with generator charging.
How big a generator do you need?
Size the generator to carry your backed-up loads and charge the battery at the same time. Here’s a planning table, with manufacturer figures where they exist and my estimates otherwise.
| System | Generator size | Source |
|---|---|---|
| FranklinWH, 1 × aPower 2 (15kWh) | ~12kW | FranklinWH recommendation |
| FranklinWH, 2 × aPower 2 (30kWh) | ~23kW | FranklinWH recommendation |
| EcoFlow Smart Home Panel 2 | 3–12kW, 120V single-phase or 240V split-phase | EcoFlow manual |
| Generac PWRcell 2 | Generac standby up to 28kW | Generac |
| 2kWh power station, 1,800W AC charging | ~2,200–3,000W inverter generator | My estimate (charging plus a margin for small loads) |
For integrated systems, follow your installer’s sizing. Enphase, for example, publishes minimum generator sizes per battery count in its planning documents.
What a day looks like (estimate)
Here’s an example for a home using about 20kWh a day in an outage (fridge, freezer, lights, internet, well pump, some cooking), with one 15kWh battery and a 12kW generator. All figures are estimates.
| Time | What runs the house | Battery state |
|---|---|---|
| 10 pm – 7 am | Battery only (quiet hours) | ~90% → ~40% |
| 7 am – 9 am | Generator carries loads and recharges the battery | ~40% → ~85% |
| 9 am – 10 pm | Battery, plus solar if you have it | Slow discharge, or holds with solar |
In this example, the generator runs about 2–4 hours a day instead of 24. That’s the main advantage of pairing. With solar on the roof, many sunny outage days may need no generator time at all.
Choosing a fuel
| Fuel | Strengths | Things to plan for |
|---|---|---|
| Natural gas | No refueling on a standby unit connected to the gas line | Needs a gas service and a permanent install |
| Propane | Stores for years in a tank; clean-burning | Tank size sets your runtime; slightly less output than gasoline on many dual-fuel units |
| Gasoline | Easy to find; most portable generators run on it | Goes stale in storage without stabilizer; cans need safe storage |
A battery stretches whichever fuel you choose, because the generator runs for fewer hours. That’s especially useful with propane and gasoline, where what you’ve stored is all you have until deliveries resume.
Safety and installation basics
- Use a transfer switch or approved interlock. Never backfeed a dryer outlet. My transfer switch vs interlock guide explains the options.
- Run generators outdoors, away from windows and doors. Carbon monoxide from portable generators is a well-documented danger.
- Check neutral bonding. As EcoFlow’s manual notes, some systems need the generator’s ground-neutral bond removed.
- Have an electrician do the wiring. Integrated systems are installed by certified installers.
FAQ
Can a generator charge a home battery?
Yes, with the right equipment. FranklinWH (with the aGate generator module), Enphase (with IQ System Controller 3G), Generac PWRcell 2 and EcoFlow’s Smart Home Panel 2 all support generators. Portable power stations charge from a generator through their AC input.
What size generator do I need for a home battery?
FranklinWH recommends about 12kW for one aPower 2. EcoFlow’s Smart Home Panel 2 supports 3–12kW generators. For a portable power station, a generator about 20–60% larger than the station’s AC charging rate works well (estimate).
Will the generator start automatically?
With FranklinWH’s generator module and Enphase’s IQ System Controller 3G, yes. Both can start and stop a compatible generator. Portable setups are manual.
Can I use a 120V portable generator?
For a portable power station, yes. EcoFlow’s Smart Home Panel 2 also lists 120V single-phase generators as compatible. Whole-home integrated systems like FranklinWH and Enphase are generally designed around 240V generators, so check with your installer.
How much fuel does pairing save?
It depends on the loads, but running a generator a few hours a day at a heavy load instead of all day at a light load can cut fuel use substantially (estimate).