Size your battery bank from real loads fast. Include surge, autonomy, and wiring current too. Export results to PDF or CSV for reports later.
| Load | Watts | Qty | Hours/day | Surge factor | Wh/day |
|---|---|---|---|---|---|
| LED Lights | 12 | 6 | 5 | 1.0 | 360 |
| Ceiling Fan | 55 | 2 | 8 | 1.3 | 880 |
| Router | 10 | 1 | 24 | 1.0 | 240 |
| Total | 1,480 | ||||
A reliable battery plan starts with a clear load list. Each item needs watts, quantity, and daily run hours to estimate watt-hours per day (Wh/day). Duty cycle matters: many tools and pumps do not run continuously, so measured hours usually beat nameplate assumptions. Include always-on electronics, charging bricks, and network gear because small loads accumulate over long hours. Keeping notes about seasonal use and standby loads makes the energy total more realistic and reduces expensive oversizing for better accuracy.
Some appliances draw a short starting surge. The surge factor converts running watts into peak watts so you can check inverter headroom and protective device limits. If peak demand is close to equipment ratings, stagger motor starts, lower simultaneous loads, or select a higher surge-capable inverter. This step improves stability and prevents nuisance trips.
When AC loads run from batteries, conversion losses increase the battery-side requirement. The calculator applies efficiency to both power and energy, keeping results conservative. Real efficiency varies with load level; very small loads can be less efficient. Consider inverter idle consumption during light-load operation, especially overnight. Matching inverter size to typical demand often increases runtime and reduces heat.
Battery capacity is not fully usable in practice. Depth of discharge (DoD) sets the usable fraction of amp-hours, supporting longer life for many chemistries. Autonomy days multiply the daily energy for multi-day backup planning. A safety margin accounts for aging, cold-temperature derating, wiring losses, and future load growth. If the system serves critical loads, choose a higher margin and verify charging capability so recovery time remains acceptable.
Using unit battery voltage and capacity, the calculator suggests series and parallel counts. Series raises voltage; parallel increases amp-hours. It also reports DC running and peak current to help evaluate cable size, connectors, and fusing. Higher voltage systems reduce current for the same power, usually lowering voltage drop and conductor cost. Always validate with manufacturer data, local electrical codes, and site measurements before installation.
Running watts are instantaneous power. Watt-hours are energy over time. Inverter sizing depends on peak watts, while battery capacity depends on total watt-hours for the chosen autonomy.
Conversion losses mean the battery must supply more power than the AC load consumes. Lower efficiency increases both DC watts and DC watt-hours, so capacity and current rise.
Use 1.0 for resistive loads. For motors and compressors, start with 1.3–3.0 based on datasheets or field measurements. Confirm against inverter surge rating and startup behavior.
Pick a DoD that matches chemistry and life targets. Conservative DoD improves longevity for many batteries, while higher DoD increases usable energy but may reduce cycle life.
Current guides cable gauge, connector selection, and fuse sizing. Higher current increases heating and voltage drop, especially at 12 V systems, so it is a key safety check.
Yes for load and storage planning. For full design, also model solar production, charge-controller limits, charging efficiency, temperature derating, and recharge time after deep discharge.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.