Don’t start with battery brands. Start with the loads you need to keep alive, how long they must run, and whether the backup system can actually deliver the power they require.
Startup values are never guessed. Verify manufacturer startup specifications for motors, compressors and pumps.
Build This in the Full Backup Calculator →How much stored energy the outage plan requires.
How fast the system must deliver that energy.
How long each load actually needs to operate.
Running watts tell you the continuous power demand. Motors and compressors may also have a separate startup requirement.
A refrigerator cycles. A router may run continuously. A microwave runs for minutes. Equivalent runtime matters more than clock time.
Add every load’s watt-hours, convert to kWh, then account for conversion losses and whatever planning margin you choose.
Keep critical basics alive first.
Add convenience after essentials fit.
These can radically change battery size.
These are transparent examples, not household averages. The calculator above is where you replace them with your own loads.
Refrigeration + internet + a few lights.
LOWER kWhAdd laptop, monitor and workday connectivity.
MORE RUNTIMEShorter clock window can reduce total energy substantially.
TIME MATTERSContinuous loads and cycling loads begin to add up.
ENERGY ADDS UPHVAC, pumps or heat can dominate both kWh and inverter sizing.
POWER MATTERSA carefully controlled essential-load plan and a “run the house normally” plan are not the same project.
Window AC, well pumps, sump pumps, microwaves, electric resistance heat and other motor or heating loads can increase energy demand, continuous power or startup requirements. Size these individually before assuming a battery can support them.
A 5 kWh battery tells you how much energy is stored. It does not automatically tell you whether the inverter can supply a 1,500 W heater, start a pump, or provide 240V output.
Determines how long loads can run.
Determines what can run at the same time.
For motors and compressors, also verify startup or surge power. For large appliances, verify voltage compatibility before doing runtime math.
Many U.S. household loads use 120V, while larger equipment may require 240V. A battery can have plenty of kWh and still be electrically incompatible with the appliance. Check the system’s output voltage, continuous power and startup capability.
Short interruptions. Prioritize refrigeration, communications and immediate essentials.
Overnight planning. Continuous loads begin to matter more.
A full day exposes the true cost of always-on and cycling loads.
Recharge strategy, weather, fuel alternatives and load discipline become increasingly important.
Use manufacturer specifications, a measured value, or a clearly marked planning example.
WHow many hours the load is actually energized during the outage.
hoursAdd watts × runtime for every active load.
Σ(W × h)Divide watt-hours by 1,000.
Wh ÷ 1000Zaron uses 90% as a planning assumption, not a universal constant.
÷ 0.90Zaron applies a 20% planning margin for headroom.
× 1.20Planning capacity before product-specific limits are checked.
raw kWh ÷ .90 × 1.20DOE technical material describes sizing electrical systems by multiplying appliance power by hours of use, then summing watt-hours across loads.
DOE sizing material →ENERGY STAR product listings provide model-specific annual energy use for certified appliances such as refrigerators.
ENERGY STAR refrigerators →Ready.gov recommends preparing for power outages and maintaining alternative charging options and emergency plans.
Ready.gov preparedness →Add the watt-hours for the loads you want to support, then account for conversion loss and planning margin. The answer changes dramatically depending on whether you are powering only essentials or high-energy loads.
There is no universal number. Twenty-four hours of internet and lighting is a very different load from 24 hours with HVAC, pumps or resistance heat.
It can be enough for selected essentials, but energy capacity alone does not guarantee that all appliances can run. Check output power, surge and voltage too.
For loads with motors or compressors, yes. Do not guess the startup value. Verify the manufacturer specification or measure it appropriately.
It is a planning assumption for conversion/system losses. It is not a universal specification. Use the actual product's usable-energy and inverter data when available.
It creates planning headroom. It is a Zaron convention, not a law of physics. You can choose a different margin for your own engineering or product-specific design.
Start with your loads, runtime and power requirements. Then compare batteries and equipment against a plan you can explain line by line.
Open the Full Backup Calculator →