Is this battery life estimate correct?

[XOIIO]

Alright so I've never really tried this before and maybe I did something totally wrong, who knows but it seems about right, if I have a circuit that uses 60ma, powered by a 9v battery which I've seen online has a capacity of 500mah, it should run for approximately 8 hours, right?

[con-f-use]

That is correct for a first estimate. No black magic to it. Though the voltage will drop before that, causing the circuit to fail. So it depends on what exactly the battery powers. Test your circuit's min. operating voltage. consult the datasheet of your battery. There should be a diagram detailing the voltage drop.

[XOIIO]

That is correct. No black magic to it. Though the voltage will drop causing the circuit to fail before that, depending on what exactly the battery powers. Test your circuits min. operation voltage and consult the datasheet of your battery. There should be a diagram detailing the voltage drop.

well, I don't think there is a datasheet for my cheapo dollar store Panasonic battery lol, but thanks.

[con-f-use]

Even cheap batteries use the same chemistry and are standardised. Find a comparable data sheet.

[IanB]

Take a look at this datasheet for a standard 9 V alkaline battery, for example:

http://data.energizer.com/PDFs/522.pdf

According to the constant current performance chart, you would get about 7 hours life at 60 mA drain down to 6 V.

As others have said, the similarities between different brands of alkaline battery are greater than the differences.