Find out how long your battery lasts
Enter the battery you have and what you connect to it, and get the days of runtime without recharging.
Your battery
Description
The details of the battery you already have. They are used to measure the energy you can really use, in watt-hours (Wh), without damaging it: from 50 % for lead batteries up to 80 % for lithium.
Your appliances
Description
Everything you will have connected. It is used to measure how much energy you use per day: watts × hours of use × units.
Tap what you will use
How long it lasts
Description
The days your battery lasts with your consumption, without any recharging. Also the hours it would last with every appliance switched on at once, which is the worst case.
You have changed some data. Press Calculate to update the result.
To understand it better
Worked example
A 100 Ah lithium battery at 12 V stores about 960 Wh of usable energy. With a compressor fridge and LED lights, which use 510 Wh per day, it lasts 1.9 days.
Typical consumption
| Appliance | Power | Use per day | Consumption per day |
|---|---|---|---|
| Compressor fridge | 45 W | 10 h | 450 Wh |
| LED lights | 15 W | 4 h | 60 Wh |
| Water pump | 60 W | 0.2 h | 12 Wh |
| Phone charging (USB) | 20 W | 2 h | 40 Wh |
| Roof fan | 25 W | 5 h | 125 Wh |
| Parking heater | 30 W | 6 h | 180 Wh |
| Router 4G | 10 W | 8 h | 80 Wh |
| Laptop | 60 W | 3 h | 180 Wh |
| TV | 50 W | 2 h | 100 Wh |
| Coffee machine | 1,000 W | 0.1 h | 100 Wh |
| Hair dryer | 1,200 W | 0.1 h | 120 Wh |
| Microwave | 900 W | 0.1 h | 90 Wh |
| E-bike (charger) | 150 W | 3 h | 450 Wh |
Indicative values. Check the label on your appliances for more precision.
Common mistakes
- Counting on 100 % of the battery. With lead batteries you should only use half.
- Entering 24 hours for the fridge. The compressor only runs part of the time, usually 8 to 12 hours a day.
- Forgetting that cold reduces the capacity of any battery.
Questions about this tool
How do I know how much charge my battery has left?
The most reliable way is a battery monitor with a shunt, which measures what goes in and out. Voltage only gives a rough idea, especially with lithium.
Why does my battery last less than calculated?
It is usually down to loads that were not listed, an aged battery or the cold. Over the years, all batteries lose capacity.
Does fully discharging the battery damage it?
With lead batteries, yes: deep discharges shorten their life considerably. Lithium batteries have electronics that disconnect them before they are damaged, but it is still best not to run them down every time.