Home batteries explained

A home battery stores electricity so you can use it later. People buy batteries for two quite different reasons: to keep the lights on during an outage, and to save money. It helps to be clear about which one you want, because the answer changes whether a battery is worth it.

Backup vs savings

Backup means the battery powers some or all of your home when the grid goes down. This needs the right equipment so your home can safely disconnect from the grid. Backup has real value, but it is hard to put a dollar figure on.

Savings means the battery shifts when you use grid power or solar power, so you buy less electricity at expensive times. This only pays when there is a meaningful price gap to take advantage of.

Many batteries do both. But a battery bought purely for savings has to earn its cost back, and that only happens under certain conditions.

Two numbers that matter

• Capacity, in kWh, is how much energy the battery holds. A 13 kWh battery can deliver roughly 13 kWh before it is empty.
• Power, in kW, is how fast it can deliver energy. A 5 kW battery can run 5 kW of appliances at once.

A battery with large capacity but low power can run a few things for a long time. One with high power but low capacity can run many things briefly. For backup, you usually need both to be adequate.

Round-trip efficiency

Some energy is lost charging and discharging. Modern lithium batteries typically have a round-trip efficiency of around 90%. Put in 10 kWh, get back roughly 9 kWh.

When a battery pays

A battery saves money when it can buy or store electricity cheaply and use it when electricity is expensive. Two situations make that work.

Big peak and off-peak price gaps

Ontario's Ultra-Low Overnight plan is a good example. From November 1, 2026, ultra-low overnight power costs 3.7 cents per kWh and weekday on-peak power, from 4 to 9 pm, costs 37.7 cents per kWh.

As an illustration: charging 11 kWh overnight costs about 41 cents. At 90% efficiency, that delivers about 10 kWh during on-peak hours, replacing roughly $3.77 of on-peak power. That is a gap of around $3.35 per weekday, before tax and the Ontario Electricity Rebate. These are energy prices only, and real savings depend on how much you actually use from 4 to 9 pm.

No credit for exports

If your solar system can't use net metering, such as a system that takes Ontario's HRSP rebate, surplus solar sent to the grid earns little or nothing. A battery lets you store that surplus and use it in the evening. See net metering vs the rebate.

When a battery usually doesn't pay

• You have full net metering and a flat or modest rate gap. The grid already acts like a free battery for your credits.
• Your evening use is low, so there is little expensive power to replace.
• You are on a Tiered plan, where the price does not change with time of day.

In these cases a battery may still make sense for backup. Just don't expect it to pay for itself on savings alone.

What batteries cost

Installed prices vary with brand, size and how much of your home it backs up. As an approximate guide, expect roughly $1,000 to $1,300 per kWh of capacity installed. Treat that as a starting point, not a quote. In Ontario, the HRSP offers a battery rebate of up to $5,000, capped at 50% of the cost.

How long backup lasts

A rough rule of thumb: running only essentials, such as the fridge, furnace fan, some lights, internet and phone charging, typically draws around 0.5 to 1 kW on average.

Large loads such as electric heating, a dryer, an electric range or central air will drain a battery far faster. Solar panels can recharge it during the day if the system is designed for backup.

Questions to ask an installer

• Which circuits will be backed up: essentials only, or the whole home?
• What is the usable capacity and continuous power rating?
• How long is the warranty, and what capacity is guaranteed at the end of it?
• Is the system set up to charge from solar during an outage?

Next step

See whether a battery changes the numbers for your home: check your roof.