Battery Backup Runtime

What is the Battery Backup Runtime?

Estimate how long a battery or inverter can support a given electrical load.

This Calcwise tool is built around the question a user is actually trying to answer. The main result explains the outcome in plain language, while the supporting figures show how the answer was produced.

How to use this calculator

1. Replace every example value with your own numbers.
2. Read the What this means guide directly under each input.
3. Check the main answer and the supporting breakdown.
4. Enable Pro mode to compare an alternate loadW scenario without losing your main inputs.

Inputs used

• Usable battery capacity — Use watt-hours (Wh), not amp-hours unless converted. Example: 1000
• Connected load — Total watts used by the devices you want to run. Example: 200
• System efficiency — Allows for inverter and conversion losses. Example: 85

Battery Backup Runtime formula

The formula is shown so the result is not a black box. Where the result is an estimate, the assumptions are stated explicitly.

Worked example

The calculator opens with a usable example: Usable battery capacity = 1000, Connected load = 200, System efficiency = 85. The live answer above shows what those sample inputs mean. Replace them with your own values to get your result.

Important assumptions and limitations

Estimate only. Use your own values and check important decisions against the relevant provider, contract or official rule.

Results should be treated as a planning aid. Real prices, platform rules, contracts, taxes, institutional policies, technical performance and other conditions can differ from a simplified calculator model.

Pro mode: compare another scenario

Pro mode changes the most decision-relevant driver while keeping the rest of your inputs fixed. This makes it easier to answer questions such as “what if this cost is higher?”, “what if I have less time?” or “what if performance changes?” without rebuilding the whole calculation.

Frequently asked questions