Free run-time tool
Power Station Run-Time Calculator
Estimate how long your stored energy can last without charging. Use appliance examples for a rough budget, or enter daily fridge energy with your own battery and loss assumptions. A runtime estimate does not establish electrical compatibility.
Already own a fridge? Measure it before buying more battery capacity.
Step 1: How big is the battery?
Start with the battery you own. Use its labeled capacity; a model name such as “1000” is not an exact watt-hour rating.
Available Wh means battery-side energy remaining above your reserve. It skips the starting-charge and reserve deduction.
Use the battery label, not a voltage measured while charging.
From the spec sheet. Lets us check the station can actually POWER your loads, not just store enough energy for them.
100% start and 20% reserve are example planning choices, not advice for every battery. Follow your battery instructions and condition. This simplified energy budget does not model lead-acid discharge-rate effects, aging or cold-weather capacity.
Step 2: What are you running?
These are illustrative draw assumptions, not measurements of your equipment. Loads run continuously in this estimate. The 12V fridge choice opens the daily-energy inputs.
Use measured daily energy or a documented average across a full day. A compressor's running watts or maximum rating is not that average. How to get a useful reading.
A battery-side reading includes the supply losses it measured. An AC plug reading includes the fridge's downstream adapter, but not the station's inverter. A station's output-energy display is also downstream of its internal conversion. Use only a measurement boundary you can establish.
90% is an editable example, not a tested AC or DC efficiency. Include only delivery losses upstream of your reading; enter idle drain separately if excluded.
Lights, devices and other equipment not already included. Appliance presets are not added in fridge mode.
Only idle draw missing from the other figures. Zero assumes none beyond what they include; 5W would add 120Wh/day.
Use what you have
Measure a representative fridge day
Start with a suitable energy counter or monitor you already have, if its instructions explain cumulative Wh or kWh and the measurement point. An instantaneous watt display or a falling battery percentage is not a full-day energy measurement. One kWh equals 1,000Wh.
- Identify the power path. Record battery to DC output to fridge, or battery to inverter to AC supply to fridge. Use measuring equipment rated for that connection and follow its instructions. Do not improvise DC wiring or open mains equipment; use a qualified installer where needed.
- Log a representative 24 hours. Note the starting and ending cumulative energy reading. Keep initial cooldown separate from an already-cold day when comparing results. Use your actual fridge/freezer setting, ventilation and normal lid openings.
- Keep the conditions with the number. Record exact model/revision, ambient temperature, setpoint, contents, openings, start/end time, measurement location and which other loads or supply losses are included. Repeat in the conditions you expect on the trip; do not apply an invented universal hot-weather multiplier.
- Use the whole battery budget. Add other equipment and excluded idle drain once. If your monitor reports the whole system, do not add those same loads again. Follow the battery and fridge manuals for reserve, charging and cutoff behavior.
No meter or clear energy record? Ask the manufacturer for a daily-energy test with stated conditions, or borrow suitable measuring equipment. The example below is a way to learn the calculation, not a reason to buy a battery for an unmeasured fridge.
A 100Ah example you can reproduce
A hypothetical 12.8V, 100Ah battery stores 1,280Wh nominally. Starting at 100% with a chosen 20% reserve leaves 1,024Wh. At an assumed 400Wh/day measured at the battery, with no additional loads, idle drain or charging, that is 1,024 ÷ 400 × 24 = 61.44 hours, about 2.56 days. At 800Wh/day it becomes 30.72 hours. These are arithmetic examples, not results for either shortlisted fridge.
Open the fridge inputs, choose “Load 100Ah example”, then calculate. Already have 1,024 usable battery-side Wh? Choose “Already available Wh” so the reserve is not deducted twice.
Sources and limits
The Victron BMV-712 operation guide explains monitor readings, changing load, synchronization and why effective battery capacity varies. This calculator is a simpler energy budget, not that monitor's battery model. The ICECO manual library and BougeRV CRPRO30 page and linked manual document model-specific power and operating instructions. Match the revision supplied with your unit. Sources checked September 16, 2026.
Still choosing a fridge? The existing 12V fridge comparison covers fit and exact models. The van power example shows why the fridge is only one part of a load list.