Amp Hour Calculator 12v

12V Amp Hour Calculator

Total wattage of all devices running simultaneously.

How many hours per day the devices will be used.

50% (Recommended for Lead-Acid/AGM) 80% (Deep Cycle AGM/Gel) 100% (Lithium LiFePO4) 20% (Conservative Lead-Acid) To prolong battery life, avoid 100% discharge on lead-acid.

Commonly 85-90% for inverters and wiring resistance.

Results

Estimated Daily Consumption: Ah

Recommended Battery Bank Size: Ah

*This size accounts for your Depth of Discharge and efficiency losses.

function calculateAh() { var watts = parseFloat(document.getElementById('loadWatts').value); var hours = parseFloat(document.getElementById('runTime').value); var dod = parseFloat(document.getElementById('dod').value) / 100; var efficiency = parseFloat(document.getElementById('efficiency').value) / 100; var voltage = 12; if (isNaN(watts) || isNaN(hours) || watts <= 0 || hours <= 0) { alert("Please enter valid positive numbers for Watts and Hours."); return; } // Calculation Logic // Amps = Watts / Volts var amps = watts / voltage; // Raw Ah = Amps * Hours var rawAh = amps * hours; // Required Ah = (Raw Ah / DoD) / Efficiency var requiredAh = (rawAh / dod) / efficiency; document.getElementById('dailyCons').innerText = (rawAh).toFixed(2); document.getElementById('recBank').innerText = (requiredAh).toFixed(2); document.getElementById('resultsArea').style.display = 'block'; }

How to Calculate Amp Hours for a 12V System

Understanding the battery capacity required for your 12V system is critical for RVs, marine applications, off-grid solar setups, and emergency backups. An Amp Hour (Ah) is a measure of charge; it tells you how much current a battery can supply for a specific duration.

The Basic Formula

The math behind 12V power calculation follows these steps:

1. Find the Amps: Divide the total Watts by the Voltage (12V).
   Example: 60W / 12V = 5 Amps.
2. Calculate Daily Consumption: Multiply the Amps by the hours of use.
   Example: 5 Amps × 5 Hours = 25 Amp Hours (Ah).
3. Adjust for Reality: Factor in Depth of Discharge (DoD) and Efficiency. If you use a Lead-Acid battery, you should only use 50% of its capacity.

Why Depth of Discharge (DoD) Matters

Not all batteries are created equal. If you drain a traditional lead-acid or AGM battery to 0%, you will likely damage it permanently. Most experts recommend a 50% DoD for lead-acid. Conversely, Lithium (LiFePO4) batteries can often be safely discharged to 80% or even 100%. This means a 100Ah Lithium battery provides much more usable energy than a 100Ah Lead-Acid battery.

Common 12V Appliance Wattage Examples

Appliance	Typical Watts	Amps (at 12V)
LED Light Bulb	10W	0.83A
12V Portable Fridge	45W	3.75A
Laptop Charger	65W	5.42A
Small 12V Fan	15W	1.25A

Efficiency Losses

No electrical system is 100% efficient. When electricity travels through wires, some energy is lost as heat. If you are using an Inverter to convert 12V DC to 110V/220V AC, you typically lose 10-15% of your power in the conversion process. This calculator uses an efficiency factor (default 85%) to ensure you don't undersize your battery bank and end up with a dead system prematurely.