What Battery For

Backup power and power stations

What size power station, backup battery, UPS or standby generator a CPAP, fridge, sump pump, RV, router or house needs.

Power station size calculatorType the watts of what you’ll run and for how many hours, and get the watt-hours a portable power station needs, with each maker’s allowance for losses. mAh to Wh calculatorTurn the milliamp-hours on a battery or power bank into watt-hours, with FAA PackSafe’s 100 Wh and 160 Wh lines for spare lithium ion batteries. Power station for a CPAPFrom ResMed’s own figures, the watt-hours an AirSense 10 needs for a night, with and without the humidifier, and ResMed’s and Philips’ battery advice. Power station for a fridgeTurn the kWh a year on a fridge’s yellow EnergyGuide label into the watt-hours a day a power station must hold, with four ENERGY STAR models worked out. Power station for campingAdd up a camping day’s watt-hours from each maker’s spec, for a 12 V fridge, Starlink and a CPAP, and the station that covers them. Power station for StarlinkPick your Starlink kit and the hours, and get the station size from Starlink’s own average power figures. Sump pump battery backupHow long a battery backup sump pump runs on one or two batteries, from Basement Watchdog’s and WAYNE’s own figures. RV house battery sizeTurn a day’s watt-hours in an RV or camper into amp-hours at 12 V, Renogy’s way, and what Battle Born says lithium changes. Trolling motor battery sizeHow many 12 V deep cycle marine batteries a MotorGuide trolling motor takes, by its thrust and volts, from MotorGuide’s manuals. UPS size for a computer or routerAdd up the watts on the UPS and multiply by 1.25, CyberPower’s rule, then check the UPS’s watt and VA ratings. Whole house generator sizePick the big loads in your home, such as central AC and a well pump, and get the standby generator size in kW by Generac’s and Champion’s methods.

Sizes at a glance

Station and battery sizes from each maker’s figures
What it runsSize or runtime
ResMed AirSense 10 CPAP, 8 hoursAt least 66 Wh
ResMed AirSense 10 with humidifier, 8 hoursAt least 208 Wh
Fridge using 366 kWh a year, 24 hoursAt least 1,180 Wh
Starlink Standard kit, 8 hoursAt least 942 Wh
12 V fridge, Starlink Mini and CPAP, a dayAbout 1,286 Wh
Basement Watchdog Big Dog CONNECT, one batteryUp to 40 hours pumping
WAYNE ESP25n, one batteryUp to 10,000 gallons a charge
MotorGuide 24 V trolling motorsTwo 12 V deep cycle marine batteries
RV: Renogy’s 35 W fan for 6 hours35 Ah at 12 V
UPS for a 200 W loadAt least 250 W
Standby generator: fridge, lights, furnace blower and 3-ton ACAt least 15.6 kW
20,000 mAh power bank at 3.7 V74 Wh, under the FAA’s 100 Wh limit

Station sizes are watts × hours ÷ 0.85, the factor Jackery, EcoFlow and Anker SOLIX use. The CPAP figures are measured watt-hours at ResMed’s test settings; Starlink’s are its top average. The standby size is the larger of Generac’s and Champion’s methods. Without a soft start on the AC, Generac’s own 3-ton AC figures put the same home at 25.1 kW.

Where we get our information from

The figures come from each maker’s own spec sheets, manuals and pages, and the flying limit from the FAA. Checked against published data from Starlink, MotorGuide, Champion Power Equipment, Jackery and EcoFlow (plus 10 more).

See all 18 sources
  • Jackery, Explorer 300 Portable Power Station (product page and FAQ)
  • EcoFlow blog, How Long Will a 3000-Watt Solar Generator Run?
  • Anker SOLIX blog, How Long Will a Power Station Last?
  • FAA, PackSafe: Lithium Batteries (last updated August 11, 2026)
  • ResMed, Power consumption of Air10 devices (1018673/1, PDF)
  • ENERGY STAR Certified Residential Refrigerators (EPA dataset)
  • Engel, MT45 Platinum Series 12/24V DC and 110/120V AC Fridge-Freezer (product page)
  • Starlink, Standard Kit specifications (PDF)
  • Starlink, Mini and Mini X specifications (PDF)
  • Basement Watchdog, Big Dog CONNECT Battery Backup Sump Pump (product page and specification table, with the BWSP)
  • WAYNE, ESP25n battery backup sump pump (product page)
  • Renogy Learn Center, Batteries
  • MotorGuide, X3 Owner's Manual (2017, PDF)
  • MotorGuide, Tour Pro Owner's Manual (8M4006373, 2023, PDF)
  • CyberPower blog, Runtime Recommendations
  • Generac, What Size Generator Do I Need? Sizing Guide (resource article, August 9, 2026)
  • Champion Power Equipment, What Size Home Standby Generator Do I Need? (October 16, 2026)
  • Champion Power Equipment, Generator Wattage Chart

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Battery sizes come from battery makers' datasheets and device makers' own manuals and help pages. Check your device's manual or the old battery before you buy. If anyone may have swallowed a battery, call the National Battery Ingestion Hotline at 1-800-498-8666 or your poison center at 1-800-222-1222 straight away.