Backup power calculators
Free, focused tools that turn device watts and battery watt-hours into buying decisions — no account, no downloads, nothing collected.
Pick the tool for your question
Battery Runtime Calculator
See how long a battery or power station will run a device, with conversion losses and a safety reserve included — not just the label math.
Best for: checking a battery you own — or one on your shortlist — against a specific device.
CalculatorPower Station Sizing Calculator
Turn “I need to run this for that many hours” into a watt-hour target, with losses and a planning reserve built in.
Best for: shopping for a new power station when you know your devices and hours.
CalculatorSolar Recharge Calculator
Estimate what a solar panel really delivers per day and how many days a full recharge takes — using peak sun hours, not label ratings.
Best for: deciding whether a panel is worth it, and how many watts to buy.
Decision wizardGear Finder
Answer six quick questions about your situation and get a suggested setup type, capacity range, and what to verify before buying.
Best for: starting from zero, before you know any of the numbers.
Which tool do I need?
- You already have (or picked) a battery. Check it against a device with the Battery Runtime Calculator.
- You know what you need to run, and for how long. Get a watt-hour target from the Power Station Sizing Calculator.
- You want solar to keep it topped up. Reality-check panel size and recharge time with the Solar Recharge Calculator.
- You’re starting from zero. Answer six questions in the Gear Finder and get a full setup suggestion.
All three calculators share the same formulas and conservative defaults — read how we estimate for the full method.
Frequently asked questions
Are these calculators free to use?
Yes. All three calculators and the Gear Finder are free, run entirely in your browser, and require no account. Nothing you type into them is collected or stored.
How accurate are the results?
They are planning estimates built on standard formulas with conservative defaults — 85% conversion efficiency, a 10% reserve, and 70% real-world solar efficiency. Real results vary with battery age, temperature, and device behavior, so treat the output as a sizing guide and always verify manufacturer specifications before buying.
What numbers do I need before I start?
Two figures cover most of the tools: your device’s power draw in watts, and a battery’s capacity in watt-hours. Watts appear on the device label or power adapter; watt-hours are on the battery spec sheet. If you don’t know a device’s wattage, the Device Wattage Library on this site lists typical ranges for common devices.