How long will it actually keep things running?
Backup is the reason most people start looking at storage and the part most likely to be described in a way that cannot be checked. Two limits govern it, they are independent, and the one people quote is not usually the one that bites.
Runtime on a full pack, no recharge
49.4hours
Both power limits are satisfied, so energy is the binding constraint and the runtime figure above is the real one.
Circuits you want kept alive
A pack held full for storms starts at a hundred. A pack cycled for arbitrage often does not.
Zero unless your inverter can island and keep producing with the grid down. Many cannot.
These wattages are typical nameplate figures we chose as starting points, not measurements of your appliances. A clamp meter on the circuit beats every one of them.
Energy tells you how long. Power tells you whether.
Capacity in kilowatt-hours divided by average draw in kilowatts gives hours. That is the arithmetic behind every runtime claim you will read, and it is correct as far as it goes. What it omits is that the same pack has a maximum rate at which it can deliver energy at all — 3.84 kW [1] for the smaller unit here, and 7.08 kW [2] for the larger.
Ask the smaller pack for a load above its continuous rating and the answer is not a shorter runtime; it is no runtime. The inverter declines. That is why this tool checks power first and only quotes hours once the load has cleared both gates.
The subtler version is the surge. Compressors, well pumps and air-conditioning condensers all draw a multiple of their running current while they start. A load that sits comfortably inside the continuous rating while running can be well outside it for the second it takes to spin up, and that second is enough. The worksheet names the largest surge among your selected circuits and flags it separately from the running total.
Quoted from the source document, retrieved 2026-08-06
“It provides a total usable energy capacity of 10 kWh and delivers 7.08 kW of continuous power, easily supporting heavy loads such as HVAC units and pool pumps.”
Both loads named at the end of that sentence are motor-driven, and the figure beside them is a continuous rating rather than a starting one — so the claim can be entirely accurate and still leave the question you arrived with unanswered, because whether a compressor gets moving at all is a different test from whether it can be carried once it is turning.
Rank the circuits before you price the pack
The most useful exercise here is not a runtime figure at all. It is deciding, in advance and in daylight, which circuits you actually want alive at three in the morning. Backing up a whole house is usually the most expensive and least necessary option; backing up the freezer, a few lights, the router and one medical device is cheap, and covers most of what a blackout actually costs a household.
| Circuit | Running watts | On for | Start-up draw | kWh a day |
|---|---|---|---|---|
| Refrigerator | 150 | 35% | 0.75 kW | 1.26 |
| Chest freezer | 100 | 30% | 0.50 kW | 0.72 |
| LED lighting, whole floor | 120 | 50% | 0.12 kW | 1.44 |
| Router, modem and a laptop | 90 | 100% | 0.09 kW | 2.16 |
| Well pump, one horsepower | 1000 | 10% | 4.00 kW | 2.40 |
| Gas furnace blower | 600 | 40% | 1.80 kW | 5.76 |
| CPAP or oxygen concentrator | 350 | 33% | 0.35 kW | 2.77 |
| Central air conditioner, three ton | 3500 | 60% | 14.00 kW | 50.40 |
Read the last column against the 10.0 kWh the larger pack holds [3]. A fridge, lights and the internet together come to well under two kilowatt-hours a day, which is several days of the essentials. Add the air conditioner and the same pack is empty before morning.
These wattages are typical nameplate figures we selected as starting points. They are not measurements of your appliances and they are editable for that reason — a plug-in energy meter or a clamp meter on the circuit beats every published table, including this one.
What an outage is worth is yours to decide
The payback tool on this site accepts an outage value and defaults it to zero. That is deliberate. A freezer of food, a night in a hotel, a spoiled work day and an oxygen concentrator are worth wildly different amounts, and no published national figure can price yours.
What we can say is how to make the estimate honestly: count the hours you actually lost last year rather than the hours you remember, multiply by the load you would want carried, and price that energy at what avoiding the disruption is genuinely worth to you. If that produces a number large enough to justify the purchase on its own, the arbitrage arithmetic elsewhere on this site is a bonus rather than the case.
- Capacity for the eveningThe savings ceiling, which sits well below most backup wishes.
- Capacity in ten yearsBackup runtime shrinks as the pack ages. By how much.
- What the quote coversCritical-load panels, islanding and the lines that get left off.
Questions this page gets asked
Why does the calculator sometimes refuse to give me an hour figure?
Because the answer would be misleading. If the circuits you selected draw more than the pack can deliver continuously, the inverter never starts them and runtime is not the constraint. Reporting eight hours for a load that will not run for eight seconds is worse than reporting nothing.
What is a start-up surge and why does it matter so much?
Motors draw several times their running current for the first second or two while they get moving. A 3500-watt condenser can call for around 14.0 kilowatts on start-up. That inrush, not the running load, is what trips an inverter — and it does it on a full charge, on the first attempt, which is exactly when you least expect it.
Will my solar keep the battery topped up during a blackout?
Only if the system is built to island — to disconnect from the grid and keep generating safely on its own. Plenty of installations cannot, and shut the array down along with everything else the moment the grid drops. If riding out a multi-day outage matters to you, that capability is a specification to confirm in writing, not an assumption.
How does a battery compare with a generator for outages?
They fail in opposite directions. A battery is silent, needs no fuel and works instantly, but it is bounded by stored energy and by continuous power. A generator runs as long as fuel arrives and starts large motors comfortably, but needs maintenance, fuel on hand and somewhere safe to exhaust. For a four-hour interruption the battery is better; for a four-day one with a well pump, it usually is not.
Provenance for every figure printed above
s4.enphase_5p.continuous_kw— Enphase Energy product page — https://enphase.com/store/storage/iq-battery-5p (retrieved 2026-08-06)s4.enphase_10c.continuous_kw— Enphase Energy product page — https://enphase.com/store/storage/iq-battery-10c (retrieved 2026-08-06)s4.enphase_10c.usable_kwh— Enphase Energy product page — https://enphase.com/store/storage/iq-battery-10c (retrieved 2026-08-06)