# How Long Will 100ah Battery Run 40W Appliance? + Calculator

A 12v 100ah lead-acid battery with a 50% DoD limit will run an appliance that requires 40W for about 13 hours

Keep reading I’ll explain how you can calculate how long will your 100ah battery run on a 40-watt appliance

## How long will 100ah battery last – calculator

Battery Capacity
Ah
Battery Volts
V
Select Battery Type
Wh

Note! use my solar panel size calculator to find out what size solar panel you need to recharge your battery in desired hours with solar panels.

### Assumptions:

• Inverter Efficiency: 90%
• Lead-acid battery: 50% depth of discharge limit
• Lithium (LiFePO4): 100% depth of discharge limit

Battery Depth of discharge DoD: is the percentage of the battery that has been discharged relative to the total battery capacity. The recommended depth of discharge limit for lead-acid, AGM, and gel batteries is about 50%. Only lithium (LiFePO4) batteries can be fully discharged to 100%.

### How To Use The Calculator

• Enter the battery capacity in amp-hours (Ah): in this case, it’ll be 100
• Enter the battery voltage: is this a 12, 24, or 48-volt battery?
• Select the battery type:  Select “Lead-acid” if you’re using a flooded or sealed (AGM or gel) lead acid battery. Select “Lithium (LiFePO4)” if you use a lithium-iron-phosphate battery.
• load Connected with inverter?: Are you using an inverter to run the load or is the load connected directly through the battery?
• Enter total load in watts: Enter the total load in watts (e.g 40 for 40 watts of output load)

After entering the information, click “Calculate” button to find out how long the battery last running a load.

## Steps To Calculate 100ah Battery Runtime On 40-Watt Appliance

Follow these steps to calculate the 100ah battery life/runtime while running a 40w load.

### Steps

1- Converter battery ah into watt-hours (Wh). to calculate the battery capacity in watt-hours use this formula

``Battery capacity in watt-hours = Battery amp-hours (Ah) * Battery Volts ``

let’s say you have a 12v 100ah battery

``100ah battery in watts = 100 * 12 = 1200 watt-hours ``

2- Multiply the battery watt-hours by the battery depth of discharge limit( Default battery depth of discharge limit, Lead-acid battery: 50% DoD limit; Lithium: 100% DoD limit ). Let’s say you have a lead-acid type battery

``Battery capacity in wh after DoD limit = 1200 * 50% = 600wh``

3- Multiply the battery capacity after the DoD limit with the inverter efficiency rate to calculate the AC watt-hours ( Most of the inverters are about 90% efficient)

``Battery AC watts = 600 * 90% = 540 AC watt-hours ``

4- Divide the battery AC watt-hours by the total load connected. Let’s say 40-watt appliance is connected to your 100ah battery

``100ah battery runtime on 40w appliance = 540 / 40 = 13.5 hours``

## How Long Will A 100ah Battery Run An Appliance That Requires 40W

here’s a chart on how long will a 12v, 24, and 48v 100ah lead-acid or Lithium battery will last on 40-watt load.

### Summary

• A 12v 100ah lithium battery will run an appliance that requires 40W for about 27 hours