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# Voltage Formula

## Voltage Formula

(OP)
Is there a simple formula for finding the voltage of a battery pack that has a constant current load at a specific time?

### RE: Voltage Formula

In one word, NO.  You need to know that condition of the battery, and charge density at time of starting discharge.

### RE: Voltage Formula

(OP)
If I had a 12V battery fully charged and want to use it with a constant current of 2 amps. for 20 mins. It looks like there should be some way other than taking the battery out to know what the approximate voltage of the battery should be. Thanks for the response, just wasn't sure if I had stated my question properly.

### RE: Voltage Formula

There is no obvious way.  The battery voltage is nearly flat until it is mostly discharged, at which time the output voltage curve dies rapidly.

TTFN

### RE: Voltage Formula

ITstuff is right.  That is one of the great properties of a battery.  Actually, when charging a battery, you actually decrease the voltage when you get closer to the fully charged state.

### RE: Voltage Formula

Sorry, I meant IRstuff.

### RE: Voltage Formula

There's too many factors that affect the battery - individual manufacturing differences, age, temperature, corrosion, etc.  Generally, the voltage will drop off slowly, and those general curves are readily published.  But you can't use those curves to predict the response of a specific battery with any accuracy.

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