As the world becomes increasingly reliant on technology, power outages can be a major disruption to daily life. To mitigate this, many homeowners are turning to home batteries as a means of ensuring they have a reliable source of energy when the grid goes down. However, calculating the right size of battery for your needs can be a daunting task. In this article, we'll explore how to determine your home battery needs by understanding watt-hours and calculating your energy requirements.

The key to calculating your home battery needs is to understand watt-hours (Wh), a measure of capacity that indicates how much electrical energy a battery stores. By knowing how much power your devices consume, you can use the Wh rating of a battery to determine how long they will run. For example, a typical LED light bulb requires about 10W to illuminate, so a 1000Wh (1kWh) battery can run that bulb for 100 hours.

To put this into context, the average US home consumes about 889kWh per month, or about 29.2kWh per day, according to the US Energy Information Administration. During a blackout, you'd need about $15,000 worth of batteries on hand to keep it running for just one day, based on a rough average of 50 cents per Wh of battery capacity. However, you really only need to keep your critical devices running for as long as the power is out.

It's worth noting that not all batteries or devices list the Wh spec; some opt for amp-hour (Ah or mAh) instead. While amp-hours multiplied by the voltage gives you watt-hours, it's a less useful spec for consumer devices because it requires knowing the voltage.

According to the most recent data available, US homes average about five to eight hours of electricity interruptions per year. But natural disasters like hurricanes and wildfires can extend outages over days. Buying a battery is therefore like buying insurance: do you spend more to cover all possible outcomes or just protect yourself against the basics? Either way, you need to calculate the watt-hours.

There are many publicly available watt-hour calculators available, including ones from EcoFlow and Unbound Solar. To determine your battery needs, identify which electrical devices are critical to you and how long they'll need to run, and then total up the watt-hours. That's how much battery capacity you'll need to survive without power.

In the real world, the actual watt-hours available to power your devices can be lower than the capacity written on the battery due to factors like age and operating temperature. And batteries aren't very useful if you can't easily access that stored energy. That's why they're often sold in the form of all-in-one power stations (aka "solar generators," if equipped with a solar charge controller) with built-in AC and DC outputs for USB devices and household appliances.

As such, it's always a good idea to hedge a bit and purchase at least 10 percent more capacity than you actually need. Most battery systems designed for RVs and homes can be easily expanded with more capacity as your needs grow. Batteries built for RVs tend to start around 1kWh and max out at around 15kWh due to space and weight concerns. Those same batteries can be used in the home, where they can be scaled almost without limit.

Vanlifers, who live in vans and travel frequently, have modest needs and tend to be keenly aware of every watt they consume. For example, the author of this article goes through about 1.6kWh per day when traveling in his modified Sprinter van. He uses a combination of fixed and portable solar panels as well as an alternator charger to juice up his energy packs, allowing him to live and work comfortably off-grid for at least four days at a time.

Charging solutions for homeowners are similar, just bigger and more expensive. Homes can be fitted with solar roofs and fully integrated battery backup systems from companies like Tesla, Jackery, EcoFlow, Anker, Bluetti, and others. They can also plug a car into the home to power it off their EV's giant battery. Otherwise, you can always keep it cheap and old school by firing up the ol' diesel generator.

Regardless of the solution you choose, it all starts with the Wh — get that calculation right, and you've taken the first step toward energy independence.