# Graph of Li-ion voltage vs. % capacity?



## Muse (Apr 1, 2007)

I know that more significant than the voltage you measure when you just take your li-ion battery off a charger is the voltage you will measure a while (say 10 minutes) later. I want to know what % capacity my battery is at by virtue of this measured voltage. Does anyone know of a chart, table, graph or other means of determining this? 

I also wonder if my various li-ion batteries are equivalent with respect to this. I have a couple of minidv camcorder batteries, a cell phone (with exposed battery terminals) and an MP3 player that all have li-ion batteries and they appear to all have maximum charge levels of something like 4.20 volts. This makes me suppose that the same table will work for all of them. TIA.


----------



## balazer (Apr 1, 2007)

This doesn't answer your question exactly, but here you can find cell voltage as a function of time, under loads down to C/5.

2400mAh LG 18650 cell discharge graph


----------



## SilverFox (Apr 1, 2007)

Hello Muse,

You may find this thread informative.

Tom


----------



## Muse (Apr 1, 2007)

SilverFox said:


> Hello Muse,
> 
> You may find this thread informative.
> 
> Tom


Yep, that's what I had in mind. Thanks.


----------



## elgarak (Apr 1, 2007)

Just to point out (Tom's/Silverfox's posted thread mentions this):

The voltage recovers once the battery/cell is removed from the load or charger.

You can use the voltage from the graphs to determine the status if there's a constant load applied (during discharge).

You cannot use the voltage to determine how much juice is left in a stored or rested battery directly, open circuit measurement.

What you could do is apply a known constant load and wait a certain time -- though I do not how fast the voltage drops. In this case you could also measure the amperage the battery is still capable to deliver. I do not know if amperage or voltage are the more reliable indicator of charge status of the battery.


----------



## SilverFox (Apr 1, 2007)

Hello Elgarak,

I think you are mixing up chemistries. With Li-Ion you can get a good indication of capacity simply by measuring the open circuit resting voltage. This does not work for Lithium, or Nickel based cells, but you can get a very good idea with Li-Ion.

Tom


----------



## elgarak (Apr 2, 2007)

You're right. I did not read your thread properly. Sorry!


----------



## LEDite (Apr 3, 2007)

Here is a State-of-Charge graph from Texas Instruments:





You should let the cells rest for an hour or two before the chart is used.

Larry Cobb

Tom- your Sanyo & Sony #18650 cells shipped UPS today.


----------

