Actual battery runtime vs online calculator

Other Hardware General Electronics
1

I had two extreamly cheap (but brand new) AA batteries that i wantet to test. I soldered a 5mm green led to the batteryes with resistor. The two batteries gived 3.2 volt when i started and the led current was measured to 4.96mA.

An online calculator gave batteries around 20 days lifetime.

I soldered the led to the batteries 3.august 2020 and today the led is still working. I measured the voltage today and that gave me 2.69V.

I'm a little impressed, for it is not common for things to work better in practice than in theory in my opinion.

Batteries is soldered in series.

Is there some good explanations for this?

2

Alkaline batteries typically have 2500 milliAmpere-hours (mAh) capacity when new, so the estimated lifetime is 2500mAh/5mA = 500 h = 20.8 days.

However, the LED current drops as the battery voltage drops, so 5 mA is an overestimate.

3

Did the online calculator ask you for the full specifications of the battery? I didn't think so.

4

I measured the voltage today and that gave me 2.69V.

What is the current now (mA)?

5

I can check current later today. I come back with the results. :slight_smile:

6

Capacity is often calculated at a certain load , and would have to be specified on the low side too .

7

I measured the current now and it was just 1mA. So you had right.

I don't think this led is light for long now. But it's still bright. :slight_smile:

8

When you soldered to the battery, it is very likely that the battery characteristics changed due to the heat. That is why tabs are spot welded to batteries, not soldered.

9

But the led has light up for 30 days now. Not bad :slight_smile:

10

The led is still going strong as we speak :slight_smile: