Estimate demand before relying on a battery.
Start with lighting, communication and the computer needed to open your information. For essential medical equipment, make a separate backup plan with the equipment provider and care team. This worksheet cannot establish a safe medical backup supply.
For a constant load, watt-hours ≈ watts × hours. A 20-watt light used for 3 hours needs about 60 watt-hours. A 50-watt laptop used for 4 hours needs about 200 watt-hours. Actual demand varies with workload and charging state.
The battery’s headline capacity is not all available at its outlets. Inverters, converters, temperature, age and reserve settings reduce usable energy. Use manufacturer specifications and a measured trial; do not assume a fixed efficiency applies to every battery.
A source with enough energy can still be unable to supply a device’s running or startup power. Check compatible voltage, output ratings, cables and connectors. Never improvise electrical connections.
Fuel-burning generators belong outdoors, far from doors, windows and vents, following current public guidance and manufacturer instructions. Never run them in a home, garage or enclosed space. Use working carbon monoxide alarms. Never backfeed household wiring.
Suppose a device draws a measured 50 watts while operating and you plan to use it for four hours. Its energy estimate is 200 watt-hours. A separate 15-watt light used for eight hours adds 120 watt-hours, making 320 watt-hours before allowing for conversion losses and reserve. These numbers are an example, not a runtime claim for a particular battery or computer. Actual laptop demand can change with workload, screen settings and charging. Use a measured trial with the equipment you will actually carry. Write down the test conditions so a later result can be compared fairly.
A battery’s energy capacity, its available output power and the rate at which it can recharge are different limits. A source may have enough nominal stored energy but an unsuitable outlet, connector or power rating. Do not compare amp-hour ratings from different voltages as though they were automatically equivalent energy capacities. Use the manufacturer’s stated watt-hour information and compatible-equipment instructions when available. Do not modify connectors, combine batteries or improvise charging arrangements to make a worksheet balance. If a specification is unclear, obtain appropriate technical advice. This planning sheet is not an electrical installation or battery-construction guide.
Make a short list of the devices that support the household’s chosen plan, then identify which can be used less often or for shorter sessions. Separate convenience loads from needs that require a professional continuity plan. For essential medical equipment, coordinate with the provider and care team; a simple percentage reserve or household generator cannot be assumed adequate. Keep a paper contact and route plan so every information task does not depend on starting a computer. Record the changes you could make safely and the assumptions that would have to be checked. Do not let a calculated estimate become a reason to ignore a device warning.
Conduct a safe ordinary trial following the equipment’s instructions. Record the source’s starting state, the connected devices, the tasks performed and the elapsed time. Note whether a computer was also charging its internal battery, because that can change the load. Stop the test at the manufacturer’s appropriate limits rather than deliberately exhausting a source or overheating equipment. Record an observed runtime as an observation under those conditions, not a guarantee for a future event. Recheck after equipment changes and significant battery aging. Keep the documented charging and storage instructions with the kit, and leave fuel-burning equipment operation to the relevant safety guidance.
Device | watts | hours | estimated watt-hours __________________ __________________ Total energy estimate: __________________ Source continuous / surge ratings: __________________ Measured runtime and test conditions: __________________