By Graham FisherThe jackery homepower 3600 pro max is a large, expandable home backup battery system, and the fastest way to decide whether it fits your needs is to total the watt-hours your critical loads will use during an outage. This guide walks through that math step by step, using a refrigerator, a CPAP machine and a sump pump as worked examples, so you can estimate runtime before you buy or set up the unit.
Sizing is less about the brand name and more about three numbers: the power each device draws, how long it runs per day, and how many hours of coverage you want. Once you have those, the rest is arithmetic. Manufacturers publish capacity and output ratings for the unit, and owners often report that real-world runtime lands below the simple math because of conversion losses, temperature and battery age. Build in a margin and you will avoid surprises.
Shopping for one? See our guide: Jackery HomePower 3600 Plus Solar Generator: 5 Best Picks Compared (2026).
Step 1: Decide Which Loads You Actually Need to Run
Start with a short list of what must keep working during an outage. Whole-house backup is a different project from powering a few critical circuits, and trying to cover everything with one portable unit is the most common sizing mistake. A practical starting list for most households includes:
- Refrigerator or freezer (food safety)
- CPAP or other medical device
- Sump pump (basement flooding risk)
- Router and modem (connectivity)
- Phone and laptop charging
- A few LED lights
- Furnace blower or well pump, if applicable
Leave out high-draw items such as electric dryers, electric water heaters, central air conditioning, and electric ranges unless you have a very large battery bank and solar input. Those appliances can drain a system in a fraction of an hour.
Step 2: Find the Wattage and Daily Energy Use of Each Device
For each device, you need two figures: running watts (the continuous draw while operating) and starting or surge watts (the brief spike when a motor kicks on). Check the nameplate sticker, the owner’s manual, or the manufacturer’s spec sheet. If only amps and volts are listed, multiply them to get watts.
Then estimate daily runtime. A refrigerator does not run continuously; its compressor cycles, so many owners use a duty-cycle figure of roughly 30 to 50 percent when estimating energy. A sump pump runs only when water rises, so daily runtime depends heavily on rainfall and basin size. A CPAP typically runs for the length of a night’s sleep.
Worked Example: Typical Loads
| Device | Running Watts (approx.) | Estimated Hours per Day | Estimated Watt-Hours per Day |
|---|---|---|---|
| Refrigerator (efficient, modern) | 100 to 150 running, cycling | 10 to 12 (cycling) | About 1,000 to 1,400 |
| CPAP machine (typical) | 30 to 60 | 8 | About 240 to 480 |
| Sump pump (1/3 HP) | 400 to 800 while running | 0.5 to 1 (varies) | About 200 to 800 |
| Wi-Fi router and modem | 15 to 25 | 24 | About 360 to 600 |
| LED lights (4 bulbs) | 40 total | 5 | About 200 |
These ranges are illustrative. Your own numbers will differ, and a CPAP ramp or humidifier setting can change its draw. Treat the table as a template for your own calculation rather than a fixed reference.
Step 3: Use a Watt-Hour Calculator to Total Your Load
Add the daily watt-hours for every device you want to keep running. Using the example above, a fridge, CPAP, router and a few lights come to roughly 1,800 to 2,500 watt-hours per day, and a sump pump adds more on wet days.
Next, plan for the outage length. If you want to cover a 24-hour outage with those loads, you need about the same figure in usable watt-hours. If you want 48 hours, double it. Then account for inverter and conversion losses, which commonly run around 10 to 20 percent, and for battery degradation over time. A simple formula:
- Daily watt-hours of all loads × hours of outage coverage ÷ 24 = raw energy needed
- Raw energy × 1.2 (loss and aging margin) = target usable capacity
- Compare the target to the unit’s rated capacity and check whether expansion batteries are needed
For a fridge, CPAP and router running a full 24 hours (around 1,800 watt-hours), the target usable capacity is about 2,200 watt-hours. A battery system rated in the multi-kilowatt-hour range can cover that comfortably, which is why this class of unit is often chosen for essential-circuit backup.
Step 4: Check Surge Capacity Before You Plug In
Energy capacity alone does not guarantee a device will start. A sump pump or a refrigerator compressor can draw several times its running wattage at startup. Confirm that the inverter’s continuous output rating and its surge rating both exceed your largest motor’s startup draw, with headroom. Plugging a high-surge motor into an undersized inverter will trip protection, and in some cases damage equipment.
Also consider how many devices will run at once. Add the running watts of everything that could be on simultaneously, not just the biggest item, and make sure the total stays under the rated continuous output.
Step 5: Plan Charging and Recharge Between Outages
Runtime is only half the story. For longer or repeated outages, you need a way to recharge. Options commonly include the grid (before an outage), solar panels, or a vehicle or generator charging input, depending on what the unit supports. Estimate how many hours of sunlight or charging time you need to replenish the daily energy used. Owners often report that solar recharge takes longer on cloudy days, so size your panel array with that in mind.
Tips and Common Mistakes
- Forgetting the sump pump’s duty cycle. Heavy rain can keep it running for hours. Estimate worst-case runtime, not average.
- Ignoring temperature. Batteries often deliver less capacity in cold weather and age faster in heat. Keep the unit in a ventilated, moderate-temperature space.
- Counting the nameplate as usable capacity. Always apply a loss margin to the rated watt-hours.
- Running a refrigerator without checking its startup draw. Verify surge headroom first.
- Leaving the battery at 0 percent. Recharge after each outage so the next one starts full.
- Assuming a CPAP has no backup needs. If you rely on one, confirm your power plan with your sleep physician or equipment supplier, and treat medical power as a priority.
Recommended gear
A few accessories make a large-battery setup easier to run safely and to monitor during an outage.
- Jackery HomePower 3600 Pro Max expansion battery: Adding expansion capacity is the most direct way to extend runtime beyond the base unit’s rating, and it is worth checking compatibility before purchase. View on Amazon
- Kill-A-Watt style plug-in power meter: A plug-in meter shows the real wattage of a refrigerator, CPAP or router, which lets you replace estimates with measured numbers. View on Amazon
- Transfer switch or interlock kit for the home panel: A properly installed transfer solution is the safe way to connect the system to hardwired circuits, and it should be installed by a licensed electrician. View on Amazon
- Extension cords rated for the load: Heavy-gauge cords reduce voltage drop and heat, particularly for a sump pump or refrigerator. View on Amazon
For a broader comparison of how this class of unit stacks up against other home backup brands, see Jackery vs Bluetti vs EcoFlow vs Anker (2026): Which Is Better for Home Backup? and EcoFlow vs Jackery vs Anker (2026): Which Is Better for Home Backup?. If you are weighing a competing platform for the same loads, Ecoflow Delta 3 Classic Review (2026): Specs, Pros and Cons covers a smaller unit that may suit lighter needs, and EcoFlow Delta Pro Ultra Battery Options Compared (2026) looks at larger battery configurations.
FAQ
How long will the jackery homepower 3600 pro max run a refrigerator?
It depends on the fridge’s efficiency and how often its compressor cycles. A modern, efficient refrigerator often uses roughly 1 to 1.5 kilowatt-hours per day, so a fully charged system with usable capacity in the range of a few kilowatt-hours can run it for a day or more. Measure your fridge with a plug-in meter for an accurate figure.
Can it run a CPAP overnight?
Typically yes. Most CPAP machines draw a modest amount of power, often in the range of tens of watts, so a night’s use uses only a small share of the battery. Confirm your machine’s wattage and any humidifier draw first.
Will it power a sump pump?
It can, provided the inverter’s surge rating covers the pump’s startup draw and you account for how long the pump may run during heavy rain. Sump pumps are a priority load for many homeowners, so plan for worst-case runtime.
Do I need to add expansion batteries?
Only if your calculated watt-hour target exceeds the base unit’s usable capacity, or if you want multi-day coverage. Run the math from the watt-hour calculator above before deciding.
How long does it take to recharge?
Recharge time depends on the input source and its wattage. Grid charging is generally the fastest, while solar recharge varies with panel size and sunlight. Check the manufacturer’s specifications for charging rates.
Can it back up my whole house?
Usually not on its own. Whole-house backup typically requires a larger system or a properly installed transfer solution. Limit the system to essential circuits unless a licensed electrician has verified the setup.
Is it safe to use indoors?
Battery systems should be operated in a well-ventilated area, away from water, and not in enclosed spaces where heat can build up. Follow the manufacturer’s guidance on placement and keep it out of direct sun.
Should I consult a professional for installation?
Yes. Any connection to your home’s electrical panel should be made by a licensed electrician to meet local code and to avoid backfeed hazards to utility workers. If you rely on medical equipment, also discuss your backup plan with your healthcare provider.
Conclusion
Sizing the jackery homepower 3600 pro max for an outage comes down to listing your essential loads, measuring their watts and daily runtime, and totaling the watt-hours with a loss margin. Check surge capacity separately, plan a realistic recharge, and keep your critical devices prioritized. Run your own numbers before you decide, and verify any panel connection with a licensed electrician.
Related reading
- 5 Best Jackery Solar Generator Homepower 3000s (2026): Expert Picks
- Jackery Solar Generator Home Power 3000: 4 Best Options Compared (2026)
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About Graham Fisher
Graham Fisher is part of our editorial team and reviews and edits our solar generators for home backup & emergencies guides, checking product details against manufacturer specifications and owner feedback.
