How long will a home battery run my house in an outage?

Divide the battery's capacity in kilowatt-hours by your load in kilowatts. A 13.5 kWh battery carrying a 1,500 watt essentials load of furnace fan, fridge, sump pump and lights lasts about 9 hours on paper. Drop the load to 800 watts and it stretches to nearly 17. Health Canada gives a full freezer about 48 hours and a fridge about 4, so a single battery covers an evening outage comfortably and a two-day one not at all.

Which is cheaper, a battery or a standby generator?

The generator, by a wide margin, and it is not close. A single-unit 10 to 13.5 kWh battery system runs $12,000 to $20,000 fully installed per Solar Elios, and a two-unit 20 to 27 kWh system $22,000 to $35,000. A 14 to 18 kW standby generator is $9,500 to $13,000 fully installed per RenoHouse, and it does not stop after nine hours. Where a battery wins is on what it does for the other 8,750 hours of the year, which is a different question from backup.

Why does the calculator say a real battery does less than this?

Because it does, and this tool will not pretend to know by how much. The runtime here is published capacity divided by your load and nothing else. In a real system, inverter conversion losses, the reserve percentage most batteries hold back so they are never fully drained, capacity fade after a few winters and the fact that a fridge compressor cycles rather than drawing continuously all move the figure. None of those is a number this register can source per product, and inserting an unsourced efficiency factor would look like precision without being any.

Can I have both a battery and a generator?

Yes, and RenoHouse prices a generator plus battery hybrid system at $25,000 to $55,000 fully installed in its Toronto guide, as its only published data point above 26 kW. The logic is that the battery carries the first minutes silently and covers brief outages entirely, while the generator handles anything long. Whether that is worth roughly double the cost of either one alone depends on how often your power goes out and for how long.

What happens to a battery in a multi-day outage?

It empties and then it waits. Without solar attached there is nothing to recharge it from until the grid returns, so a battery gives you one fixed budget of energy per outage rather than a supply. With solar attached it recharges each day, but only as much as the panels make, which in a Toronto January is a fraction of a summer day. A generator on the natural gas main is the opposite case: it does not store anything, and it does not run out either.

Home Battery vs Generator: Runtime Calculator

How long does the battery actually last?

Your essential loadwattsFurnace fan, fridge, sump pump and lights come to roughly 1,500 W. The sizing calculator works out yours.Battery sizePublished nameplate capacity. A real system delivers less than this.Outage you want to ride outhoursHealth Canada gives a full freezer about 48 hours and a fridge about 4.Is the battery going in with a NEW solar system?This decides whether the Ontario rebate applies at all. Most people asking this question answer no.

Battery runtime on your load

9.0 hours

That does not cover the outage you asked about. This is the whole difference between the two: a battery holds a fixed number of kilowatt-hours, and a generator on the gas main does not run out.

Battery, fully installed (Solar Elios, Canada): $12,000–$20,000
Ontario HRSP rebate (Home Renovation Savings Program): $0
Battery, after rebate: $12,000–$20,000
A 14 to 18 kW standby generator, fully installed (RenoHouse, Toronto, 2026 guide): $9,500–$13,000

Rebate: Nothing. The Home Renovation Savings Program requires battery storage to be paired with a new solar PV system and sized to it, so a battery installed purely for outage backup does not qualify.

Runtime is the battery's published capacity divided by your load, and nothing else. Inverter losses, the reserve most systems hold back, and capacity fade after a few winters all make a real system do less than this, and none of them is a figure this register can source per product. An unstated efficiency fudge would look like precision and would not be any.

The rebate condition most pages leave out

Ontario's Home Renovation Savings Program pays $300 per kWh on battery storage, capped at $5,000 and at half the total cost. Plenty of guides publish that rate. Far fewer publish the sentence next to it on the program's own page: battery storage systems must be paired with a new solar PV system and sized appropriately for the solar system being installed, and are meant primarily to store what the panels generate rather than power from the grid.

For the person asking whether a battery beats a generator for outages, that condition usually means the rebate is zero. It is an input on this calculator rather than a footnote for exactly that reason. The program also notes that taking the incentive rules out a net-metering agreement with your local utility on the same system, which is a second thing worth knowing before committing.

This register previously carried that per-kWh figure sourced to a third-party rebate guide, with a note saying it was unconfirmed. It was checked against the program's own page on 25 August 2026, and the rows and the home battery cost guide now cite the program directly, with the solar-pairing condition attached.

What each one is actually good at

A battery is silent, instant and has no fuel line. It takes over inside a fraction of a second, so a brief cut is something you notice only because a light flickered, and it does not need an annual service visit or a weekly self-test that wakes the neighbours. For the short outages that make up most of what the GTA actually sees, it is the nicer machine by a distance.

A generator is the one that does not run out. Its advantage is entirely about the long tail: the ice storm, the multi-day rural outage, the week when the battery would have emptied on the first evening. It also costs less to install than a battery system of any useful size, which surprises people who assume the machine with moving parts and a gas line must be the expensive one.

Our home battery versus standby generator comparison sets the two out side by side across every criterion. If the generator is winning for you, the sizing calculator gives you the kW figure to shop with, and the outage cost calculator puts a number on what you are protecting against.

Frequently asked questions

How long will a home battery run my house in an outage?: Divide the battery's capacity in kilowatt-hours by your load in kilowatts. A 13.5 kWh battery carrying a 1,500 watt essentials load of furnace fan, fridge, sump pump and lights lasts about 9 hours on paper. Drop the load to 800 watts and it stretches to nearly 17. Health Canada gives a full freezer about 48 hours and a fridge about 4, so a single battery covers an evening outage comfortably and a two-day one not at all.
Does Ontario's rebate apply to a battery bought just for backup?: No, and this is the single most misunderstood thing about it. The Home Renovation Savings Program pays $300 per kWh for battery storage, up to $5,000 and up to 50 percent of total costs, but the program's own page states that battery storage systems must be paired with a new solar PV system and sized appropriately for it. A battery installed purely to ride out outages, with no solar going in at the same time, qualifies for nothing. Several third-party rebate guides quote the per-kWh rate without that condition attached.
Which is cheaper, a battery or a standby generator?: The generator, by a wide margin, and it is not close. A single-unit 10 to 13.5 kWh battery system runs $12,000 to $20,000 fully installed per Solar Elios, and a two-unit 20 to 27 kWh system $22,000 to $35,000. A 14 to 18 kW standby generator is $9,500 to $13,000 fully installed per RenoHouse, and it does not stop after nine hours. Where a battery wins is on what it does for the other 8,750 hours of the year, which is a different question from backup.
Why does the calculator say a real battery does less than this?: Because it does, and this tool will not pretend to know by how much. The runtime here is published capacity divided by your load and nothing else. In a real system, inverter conversion losses, the reserve percentage most batteries hold back so they are never fully drained, capacity fade after a few winters and the fact that a fridge compressor cycles rather than drawing continuously all move the figure. None of those is a number this register can source per product, and inserting an unsourced efficiency factor would look like precision without being any.
Can I have both a battery and a generator?: Yes, and RenoHouse prices a generator plus battery hybrid system at $25,000 to $55,000 fully installed in its Toronto guide, as its only published data point above 26 kW. The logic is that the battery carries the first minutes silently and covers brief outages entirely, while the generator handles anything long. Whether that is worth roughly double the cost of either one alone depends on how often your power goes out and for how long.
What happens to a battery in a multi-day outage?: It empties and then it waits. Without solar attached there is nothing to recharge it from until the grid returns, so a battery gives you one fixed budget of energy per outage rather than a supply. With solar attached it recharges each day, but only as much as the panels make, which in a Toronto January is a fraction of a summer day. A generator on the natural gas main is the opposite case: it does not store anything, and it does not run out either.

Where these figures come from

Battery and generator prices from named Canadian suppliers and contractors, the rebate rules from the Ontario program's own page, and the food-safety windows from Health Canada. The runtime arithmetic needs no source: hours equals kilowatt-hours divided by kilowatts, which is what a kilowatt-hour means. Home Generator Index publishes the inputs and does nothing to them in between.

Home Battery or Generator? Start With How Long It Lasts