How long can I run a 1200w car amp on a 12v 50ah battery?

As the comment thread states, you can make a guess, but it might be wildly off.

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If you measure the current that is being pulled in a 'typical' use case, then your wattage becomes much less of a variable.

Watts = Volts * Amps
Watt*hours = Volts * Amp * hours

Watt-hours in battery = 12V * 50A-hours = 600Wh

This assumes that the battery actually stays at 12V (it doesn't). You can measure the voltage drop as you run the battery down to further remove this variable. Most 12V batteries are nearly out of energy when they are at 12V. Consult your manufacturers data sheet for details and adjust accordingly.

So, we have 600Wh of energy in our battery. If we run it at W, then we have 1/2 hour of energy in our battery. If we run it at 600W, then we have 1h of energy in our battery. If we run it at 300W, then 2h ... and so on ...

W-h / W = hours

The precision with which you measure voltage and current - along with the useful life of the battery - will determine how close you get to the real-world value.

Do you have a 12v device you need to power but don't know what 12-volt battery you need? For those running a continuous 12-volt load, an adequately sized deep-cycle battery is a must.

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Further reading:
TCXO vs OCXO

This calculator is designed to provide an appropriately sized AH (Amp Hours) rated battery without excessively discharging the battery below 50%.

So, if you know how much power your application takes to run and how long you would like to run it. Then plug those figures into the calculator, and we will give you our recommended AH rating you need to look for!

Remember, if you use a power inverter, you must first convert the AC Amps to DC Amps before using this calculator.

Battery Capacity Needed

12V Load Watts OR Amps Time Hours Amount of time you want to run your load. Factors Battery temperature
below 0° or over 85° F Battery over 6 months old Type AGM Flooded Gel

Result

With a safe 50% max discharge level.

Choose Your Deep Cycle Battery

(Note* if you are running AC devices, you will need to figure out the DC amperage using our DC to AC calculator).

(Note** if you are using Gel batteries in temperatures below 0 deg F but above -60 Deg F, there is no need to check the box.)

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