The four numbers that decide it
Skip the brand arguments. Four figures settle almost every case: what a watt of output costs, what a stored kilowatt-hour costs, how long it takes to refill, and whether you are allowed to run an engine where you are standing. The prices below are typical street prices from our reference data, indicative rather than quotes, so treat them as a shape rather than a shopping list.
The short version: a 7,500 W generator costs about 14 cents per running watt. A 3,600 Wh battery station costs about 78 cents per watt of output. That is a factor of five, and it widens as the job gets bigger. Work out your own load first with the watts and runtime calculator, then come back and apply the four tests.
Cost per watt: the engine wins
| Generator class | Running | Starting | Tank | Run time at half load | Typical price |
|---|---|---|---|---|---|
| 1,000 W inverter | 900 W | 1,000 W | 0.60 gal | 7 h 50 min | $350 |
| 2,200 W inverter | 1,800 W | 2,200 W | 0.95 gal | 6 h 15 min | $600 |
| 3,500 W inverter | 3,000 W | 3,500 W | 1.8 gal | 7 h 5 min | $900 |
| 5,000 W | 4,500 W | 5,000 W | 4.0 gal | 9 h 20 min | $700 |
| 7,500 W | 7,000 W | 9,000 W | 6.6 gal | 9 h 55 min | $950 |
| 9,500 W | 8,500 W | 11,000 W | 6.6 gal | 8 h 10 min | $1,200 |
| 12,000 W | 11,000 W | 15,000 W | 8.3 gal | 7 h 55 min | $1,800 |
| 15,000 W | 12,000 W | 15,000 W | 10 gal | 8 h 45 min | $2,400 |
Divide price by running watts and the pattern is clear. Small inverter generators are the expensive ones: 39 cents per watt at the 1,000 W size, 33 cents at 2,200 W, 30 cents at 3,500 W. You are paying for quiet and for a light box. The cheapest watts on the market sit in the open-frame middle: about 16 cents at 5,000 W and 14 cents at both 7,500 W and 9,500 W. Only at 15,000 W does the figure climb back to 20 cents.
Batteries move the other way. Cost per watt of inverter output is 39 cents at the 1,000 to 1,150 Wh class, 58 cents at 2,000 Wh, 78 cents at 3,600 Wh and $1.17 at the 5,000 Wh expandable class. The one point where a battery matches an engine on price per watt is that 1,000 Wh class, and it holds barely an hour of a real kitchen load.
Cost per stored kilowatt-hour
| Battery class | Capacity | Output | Surge | Typical price |
|---|---|---|---|---|
| 300 Wh class | 300 Wh | 300 W | 600 W | $250 |
| 700–800 Wh class | 750 Wh | 800 W | 1,600 W | $500 |
| 1,000–1,150 Wh class | 1,000 Wh | 1,800 W | 2,700 W | $700 |
| 2,000–2,050 Wh class | 2,000 Wh | 2,400 W | 4,800 W | $1,400 |
| 3,600 Wh class | 3,600 Wh | 3,600 W | 5,400 W | $2,800 |
| 5,000 Wh and up (expandable) | 5,000 Wh | 3,600 W | 5,400 W | $4,200 |
Price divided by capacity lands between $650 and $840 per stored kilowatt-hour at every size in the table, and the largest unit is the worst of them at about $840. Storage does not get cheaper as you buy more of it. That is the single fact that decides the big jobs.
A generator's storage is its tank, and here the comparison stops being close. A 7,500 W unit carrying 3,500 W burns 0.665 gallons an hour and empties its 6.6 gallon tank in 9 h 55 min. That one tank delivers roughly 35 kWh, about seven times the capacity of the largest battery in our list, and refilling it costs the price of six gallons of gas. Above roughly 3 kWh of stored energy, a battery costs several times a generator of the same output. Say it plainly and the decision usually makes itself.
Refuel time against recharge time
A generator refuels in the time it takes to pour a can. A battery does not refuel at all: it recharges. From a wall outlet that is hours, and if the wall outlet is dead because the power is out, it is hours you do not have.
Solar changes the arithmetic for multi-day use, but it adds hours, not minutes. Refilling a 5,000 Wh unit at 400 W of panel needs over twelve hours of good sun, which is arithmetic on the capacity, not a manufacturer claim. For a weekend off grid that is fine. For a 72 hour ice storm it is not.
Where you are allowed to run it
None of the above matters if an engine is banned. An engine is usually ruled out for:
- Indoor events, trade shows and church halls, where exhaust is a safety issue rather than a preference.
- Permitted farmers markets and street fairs, many of which prohibit generators in the vendor agreement.
- RV parks with posted quiet hours, typically 10 p.m. to 8 a.m.
- Overnight medical equipment beside a bed, where the noise is the problem even outdoors.
- Apartment balconies, tailgate lots with noise rules and anywhere near a window or vent.
In those settings the battery is not the better value. It is the only legal option, and the price per kilowatt-hour is simply the cost of being allowed to trade.
Can a power station run a fridge?
Yes, and refrigeration is the job batteries do best. A standard refrigerator draws 150 W when the compressor runs, but it only runs about a third of the time, so the honest figure is 55 W average. A 1,000 to 1,150 Wh station carries it roughly 16 hours, and a 700 to 800 Wh unit about 12.
The catch is the spike, not the energy. That fridge peaks near 750 W for a fraction of a second, which is more than the 600 W surge ceiling on the 300 Wh class. The small unit fails on start-up while showing plenty of charge left. If that surprises you, read starting watts versus running watts before you buy anything.
Two worked examples
A market stall running lights, a food warmer, an undercounter fridge and a card reader draws 1,350 running watts and uses 3.62 kWh over five hours. That fits one 5,000 Wh class station at about $4,200, against a 3,500 W inverter generator at about $900. Four times the money, and vendors still choose the battery, because the market rules leave them nowhere to put an engine.
A food truck is a different planet. Fryer, griddle, two refrigerators, a hood fan and a hand-wash heater come to 9,300 running watts, a 10,500 W peak and 30.8 kWh across an eight hour service. Allowing for inverter losses and a little reserve, that is 41.6 kWh of battery: nine of the largest expandable units, roughly $37,800. Or a 15,000 W generator at about $2,400. Cooking equipment is resistive and relentless, and no battery budget survives it.
The hybrid setup, which is what most people end up with
Pair them. Run the battery when noise matters and the generator when it does not.
A refrigerator and a chest freezer together draw 270 W running, spike to 870 W and average 90 W, which is 2.22 kWh a day. A 2,000 Wh class station holds them for 18 h 50 min in silence. A 2,200 W inverter generator carrying the same pair sips 0.048 gallons an hour and runs 19 h 45 min on its 0.95 gallon tank, so one gallon a day keeps the food cold and tops the battery back up in the afternoon.
That is the pattern: battery overnight and during quiet hours, generator in daylight to refill it and to cover anything that heats. It costs less than a battery bank and annoys fewer neighbors than an engine running all night. Before you buy either half, size the load with the calculator and check how long your generator will run on a tank at the load you actually have.