Your battery is an energy tank. Here’s what determines how fast it empties — and the simple habits that can keep your home running far longer.
In Part 1 of this series, we covered how to size battery storage for your home and how solar and storage work together to provide backup power. The natural next question homeowners ask is: “How long will my battery actually last during an outage?”
The answer comes down to one key factor: how much power your home is drawing at that moment. Your battery is essentially an energy tank — the faster you use it, the faster it empties. The good news is that most homes can dramatically extend battery runtime with a few simple habits once the grid goes down.
The Simple Rule for Battery Runtime
Usable battery kWh ÷ average home load (kW) = hours of runtime
Example: a 20 kWh battery at 2 kW average draw → ~10 hours
That formula sounds almost too simple, but it’s genuinely the right mental model. The variable you have the most control over during an outage isn’t your battery size — it’s your load. Cutting average home consumption from 3 kW to 1.5 kW can nearly double how long your system lasts.
| Battery Size (usable) | Average Home Load | Estimated Runtime |
|---|---|---|
| 10 kWh | 1 kW | ~10 hours |
| 10 kWh | 2 kW | ~5 hours |
| 15 kWh | 1 kW | ~15 hours |
| 15 kWh | 1.25 kW | ~12 hours |
| 20 kWh | 1.5 kW | ~13 hours |
| 20 kWh | 2 kW | ~10 hours |
For most homes, the goal during an outage is to keep average usage between 1–3 kW. At those levels, many systems can comfortably carry a home overnight until solar begins recharging the battery again the next morning.
“The variable you control most during an outage isn’t your battery size — it’s your load.“
What’s Actually Using Your Power
Not all appliances are equal when it comes to battery draw. Understanding rough power consumption helps you make fast decisions during an outage about what to run, what to limit, and what to shut off entirely.
| Device | Typical Power Draw | Outage Recommendation |
|---|---|---|
| Refrigerator | 100–200 W avg | Keep on |
| Freezer | 50–150 W avg | Keep on |
| Internet / Wi-Fi router | 10–30 W | Keep on |
| LED lighting | 30–100 W | Keep on |
| Laptop / phone charging | 30–100 W | Keep on |
| Well pump | 750–1,500 W | Use carefully |
| Microwave | 600–1,200 W | Use carefully |
| Coffee maker / toaster | 800–1,500 W | Use carefully |
| Space heater (one zone) | 750–1,500 W | Use carefully |
| Electric water heater | 3,000–4,500 W | Avoid |
| Clothes dryer | 4,000–6,000 W | Avoid |
| Electric oven / range | 2,000–5,000 W | Avoid |
| Central AC | 3,000–5,000 W | Avoid |
| EV charging | 7,000–11,000 W | Avoid |
The Backup Mode Mindset
During an outage, it helps to think of your home the way you’d think about a boat or RV running on stored energy. You’re not shutting everything down — you’re being intentional about what runs when. The goal is keeping average load under 2 kW so your battery lasts through the night and solar can fully replenish it the next day.
| Keep Running | Use Carefully | Usually Avoid |
|---|---|---|
| Refrigerator & freezer | Well pump | Electric water heater |
| Internet & Wi-Fi | Microwave (short bursts) | Dryer |
| Phone & laptop charging | Coffee maker or toaster | Electric oven or range |
| LED lighting | Small cooking appliances | Central AC |
| Furnace blower | One heating or cooling zone | EV charging |
| Essential outlets | TV | Pool or spa loads |
Watching Your Battery in Real Time
Modern solar-plus-storage systems include mobile apps that show real-time energy flow. During an outage, this becomes one of your most useful tools — you can see exactly what your home is drawing, how much solar is coming in, and your battery’s current state of charge.
Your energy dashboard during an outage
If the app shows 3–4 kW of home usage, you know the battery is draining quickly. Reduce to 1–2 kW and you’ll immediately see the estimated runtime extend. Use the app to time heavier loads — like running the well pump or a microwave — during midday hours when solar production is at its peak.
Solar Makes the Battery Last Much Longer
If your system includes solar panels, they begin recharging the battery once the sun rises — and this changes the calculation entirely. Rather than a one-time tank of stored energy, you have a daily recharge cycle working in your favor.
The typical pattern during a multi-day outage looks like this: the battery carries the home overnight, solar refills it during the day, and the battery takes over again through the evening. With reasonable energy management, this cycle allows homes to remain powered for days rather than hours — even on partly cloudy winter days in the Northeast.
“With solar recharging daily, you’re not just running on a tank — you’re running on a tank that refills itself every morning.“
The Key to Multi-Day Outage Resilience
Keep average load under 2 kW during the night and early morning. Let solar take over as much load as possible during the day. Reserve the battery for evening and overnight. With a well-sized system, this rhythm can sustain a home through extended outages with no generator required. Want to know exactly how long your specific battery and solar setup would last based on your home’s load profile? Venture Home’s energy advisors can model your system against real outage scenarios. Get in touch for a free energy assessment.