Re: ATM batteries for LED

["Dave McCarter" <dmccarter@sympatico.ca>]

> Does the resistance of the batteries come into play anywhere?
> Would two new AA cells be as bright as two new D cells?

If the current draw is low, like the 10 to 20mA we are talking about, then
the short answer is no.

The internal resistance of a _new_ battery is very low, typically a few
milliohms, so the external resistance of several hundred ohms is very
dominant. But when the battery is very old the internal resistance rises and
this is why we throw them into the recycle bin. The C or D cells have lower
internal resistance when old, which is why they can deliver current longer.

I am using two AA batteries in my homemade quad high brightness LED
observing light, with a variable resistance so I can preserve my night
vision. It gets a lot of use, and the same batteries have been in there
since '97.

Dave