Low Battery Voltage Warning Suggested Numbers?

Batteries and Chargers Rechargeable Batteries
1

Hi all,

I’m busy trying to get numbers for low battery warnings for various cell combinations and was wondering if people more knowledgeable than me (which is not hard) would be so kind as to verify or correct me in regards to the numbers I have come up with below. The data reads as battery configuration > voltage > % left. How much current is being pulled at these voltages also has a great deal to play I guess so note that at any listed value a maximum of 15W of power is required, hence the maximum current being pulled at each respective voltage is represented in brackets:

1S Lithium Ion > 3.12V > 10% (4.8A)

1S Lithium Ion > 3.06V > 5% (4.9A)

1S Lithium Ion > 3.00V > 0% (5A)

2S Lithium Ion > 6.12V > 10% (2.45A)

2S Lithium Ion > 6.06V > 5% (2.48A)

2S Lithium Ion > 6.00V > 0% (2.5A)

2S Lithium Primary > 3.42V > 10% (4.39A)

2S Lithium Primary > 3.34V > 5% (4.49A)

2S Lithium Primary > 3.2V > 0% (4.69A)

Typical batteries used above would be 18650s and CR123’s.

Am I close or completely wrong? Batteries are not my strong point to say the least. Some numbers are subjective so I just studied a few discharge graphs and decided what I thought would be best...

Any help would be appreciated.

Thanks,

- - Matt

2

For LiIon it depends on actual LiIon chemistry, here is two examples:

One is about empty at 3.1 volt and the other has lot of capacity left.

You can try comparing some more batteries in my comparator.

When measuring without load, the values are different.

3

hmmm - so there's no sort of 'generic' value that I can use for each cell type? Or rather it varies too much for me to be able to assign a generic value?

On one hand a 3V cut-off may result in lost run time, but on the other it guarantees protection for cells without their own built-in protection...

4

In the datasheet for LiIon batteries the typically low voltage values are 2.5 volt, 2.75 volt and 3 volt.

At high current it is usual not a problem to discharge below the specified cutoff voltage, but do not do it at low currents.

5

OK sweet. I might leave it at 3V until I can experiment a bit more with batteries and see how they generally used brands behave with my 3V cut off. If it's too short I'll go to 2.7V, but certainly no lower.

Thanks.