# Battery Life Test for circuit using coin cell.

Discussion in 'General Electronics Chat' started by Andrew216, Jul 5, 2016.

1. ### Andrew216 Thread Starter New Member

Jun 24, 2015
29
2
Hello Everybody!
I have a circuit that I will be running off of a coin cell battery (most likely a 2032). I would like to determine how long this battery will last in real life and not just based off calculations. Most of the time the circuit will be sitting idle and about 5-6 times a day the circuit will turn on for 15 seconds. Any suggestions on a way to test the battery life without taking any exhausting measures? Will leaving it powered all the time until the battery runs out be a good test or are there different ways to go about this?? If a schematic will help I can post it but wasn't sure if it would aid in my question.

2. ### EM Fields Member

Jun 8, 2016
254
45

Attaching a schematic to one's query is never a bad idea.

You can't determine the life of the cell without doing at least one calculation, the brute force way being to turn ON your widget, noting the time at its turn-on, then running it until it goes belly-up, noting that time, and then figuring out how much time elapsed between tSTART and tBELLY-UP. Note that in order to determine tBELLY-UP, there'll have to be someone - or something - there to witness the failure and do the time stamp.

There are other less Attila-the-Hun-like methods, but the degree of sophistication needed to implement them would depend on what you meant by: ... "without taking any exhausting measures."

For example, if you knew the duty cycle and the ON and OFF currents of your widget, you could determine its average current draw and, knowing the cell's capacity, determine the cell's life under load.

Last edited: Jul 5, 2016
3. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,854
968
Measure the current while your circuit is running.
This is the amp portion of a batteries rated amp hours
Now use your ON time and start adding up the seconds till you reach the stated capacity.
Your battery should be dependable (but won't be) for however many days it took to add up to its stated amp hour capacity.
Cut that figure in half and you will be close to real life dependability.
For a CR2032; stated capacity is .24 amp hours, or 240 milliamp hours.
If your circuit uses 120 mA and takes 1 week of operation to get to 1 hour of total on time. Then the battery would last 2 weeks.
Cut that in half and you have it. 1 week.
Do the calculation and then run a test. We can only
supply suggestions. You have to do the work, so...

4. ### Kermit2 AAC Fanatic!

Feb 5, 2010
3,854
968
You might get close to the rated capacity because your circuit let's the battery rest for long periods between use. This kind of use is easier on the battery chemistry than constant load use.

Sep 24, 2015
634
112