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What is the mathematical formula to calculate the voltage of a (typical) LiPo battery as a function of it's charge, current flowing and external temperature?

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  • \$\begingroup\$ Do you have any specific battery in mind? \$\endgroup\$
    – user17592
    Sep 12, 2013 at 11:54
  • \$\begingroup\$ I know that each battery has different parameters, however, as for MOS transistors and other components, maybe there is a general formula to calculate voltage, by varying only parameters. Am I wrong? \$\endgroup\$
    – HAL9000
    Sep 12, 2013 at 11:57
  • \$\begingroup\$ Batteries are extremely non-linear. Accurate equations if they have ever been published will be non-linear and differential. Batteries even exhibit "memory" effects depending on previous use. The equations if published will vary wildly between manufacturers. I suspect that there is no single equation for what you are looking for. Most calculations for batteries rely on simple analytical assumptions of capacity and the expected current you intend to draw. \$\endgroup\$
    – Steinar
    Sep 13, 2013 at 9:27

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Whilst I cannot provide you directly with a "generic" forumula that will solve your answer I'd suggest you perform an experiment like the one completed in this youtube video. You'll need to insulate the battery in a fixed environment at a temperature you are keen to analyse.

http://www.youtube.com/watch?v=ln8Mlz4NsW8

With the raw data you will be able to derive an equation. I highly suspect that you'll find huge variances based on the number of charges the LIPO has gone through and I suspect your results will vary based on LIPO age as well.

http://chemistry.about.com/od/howthingsworkfaqs/f/coldbattery.htm

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I am also after such equation for my 6-pack 21700 5000mAh Lipos. My system consists of a Raspberry Pi 4 and a 7" HDMI screen. I made an experiment recording the battery voltage every x seconds (x being 30) with a 700mA constant dischage.

You can see below that the "curve" is mostly a straight line (but not enterely) (y is voltage, x is readings). I am sticking with that and you could do the same, test the discharge of it with the current you are planning to consume.

enter image description here

Of course this would be an approximation, because as have been mentioned such discharge is highly non-linear.

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