Battery Runtime Calculator
Add your electrical devices, enter your battery bank specs, and instantly see how many days of power you have and how many solar watts you need to recharge in a day. Nothing uploaded.
Device Breakdown
Learn more: battery runtime and solar sizing
Calculating days of autonomy - from daily consumption to battery size
Days of autonomy is how many days your system can run without charging. To calculate it, first find daily energy consumption in watt-hours (Wh) by multiplying device wattage by hours used per day and summing all devices. Then multiply battery voltage by capacity (Ah) to get total Wh, then multiply by your depth of discharge setting (as a percentage) to get usable Wh. Divide usable Wh by daily Wh to get days of autonomy. For example: 1000 Wh daily consumption, 48V 100Ah battery with 80% DoD = 48 × 100 × 0.8 = 3840 usable Wh = 3.8 days of runtime.
Depth of discharge (DoD) and battery chemistry - how far you can safely drain
Depth of discharge is how much of your battery's capacity you use before recharging. LiFePO4 batteries tolerate 80% DoD but should not go below 20% state of charge, while lead-acid and AGM batteries should only be discharged to 50% DoD. Discharging lead-acid below 50% dramatically shortens lifespan. The calculator uses appropriate DoD defaults by chemistry - for the same physical battery, LiFePO4 gives 80% usable capacity versus only 50% for lead-acid, making LiFePO4 more cost-effective despite higher upfront cost.
FAQ
How do I calculate solar panel watts needed?
Divide your daily Wh consumption by average peak sun hours at your location (typically 4-6 for most regions). For 1000 Wh daily consumption and 5 peak sun hours: 1000 / 5 = 200 W of solar. Add 20-30% more for real-world losses from clouds, shading, and temperature effects.
What is inverter efficiency and why does it matter?
An inverter converts DC power from your battery to AC power for standard appliances. Most inverters are 85-95% efficient, meaning some energy is lost as heat. The calculator divides daily consumption by inverter efficiency (as a decimal) to account for this loss. A 90% efficient inverter means you need 1000 / 0.9 = 1111 Wh from your battery to get 1000 Wh of AC power.
Why does my actual runtime not match the calculated estimate?
Real-world factors reduce runtime: battery temperature (cold reduces available capacity), inverter parasitic draw (standby load), wiring losses, and variation in actual device usage. The calculator provides an ideal estimate - expect 10-20% less runtime in practice, especially in cold weather or cloudy conditions.