# how can I check battery health in an embedded system

I'm working on an IOT system powered with 30Ah battery (from 4.2 volt to 3.1 volt). I'm checking battery charge level by measuring the battery voltage.

now I'm looking for a way to measure battery health over time. what should I measure to determine the battery health???.

• Battery health is usually an estimate or what is more accurate: determine the battery's actual capacitance. New it's 30 Ah equals 100% health. After 2 years it could be 15 Ah equals 50 % health. To measure the actual capacity you need to integrate (multiply time and current and add up) the current over a full discharge cycle. Apr 7, 2016 at 9:15
• May be you should determine the time taken by your battery to charge upto a particular point for different times and then make an average of that times and then compare this time with the time taken to charge up to the same point when it was healthy and find whether it is healthy or not. You can also do this with discharge time too... This might need a good algorithm... I am not so sure about this but had an idea to mention it here. Apr 7, 2016 at 9:41

For a rough estimation, you could just assume that the (average) power consumption of your device remains constant over time.

Then differentiate: dV/dt. Sounds complicated but means just: Measure Vbat at some regular interval (e.g. once per minute, then average over several measurements).

From that you can determine how long it took for the battery to discharge from, say, 4V to 3.5V. (That value (e.g. in Volts per minute) is actually the dV/dt we want.)

You do this initially when the battery is new and take the time measured as a baseline, and then during operation of the device to get a value to compare against this baseline.

Later during operation, when you detect that the above discharge takes only, e.g., 25% of the time it took when the battery was new, you can infer that the battery is close-to-dead and needs to be replaced.

Of course, if the average power consumption of your device changes at some point in its life (hardware/software update,...) the original baseline value becomes meaningless and a new baseline calibration needs to be performed.

The State of Health of the battery can be determined by either the cell impedance or the cell conductance. Others advocate measuring several cell parameters, all of which vary with the age of the battery, and making an estimation of the SOH from a combination of these factors. Examples are capacity, internal resistance, self-discharge, charge acceptance, discharge capabilities the mobility of electrolyte and cycle counting if possible.

• mmm thanks for you answer but it's too complicated. the only think I can to is to measure battery voltage. with battery voltage can I determine battery life??? :) Apr 7, 2016 at 9:32
• @MakhloufGharbi The battery life is determined by the number of charge/discharge cycles under given conditions (usualy specified in the datasheet). If your battery is used in the same conditions you can estimate the life of your battery. But at least you need to add two other parameters to the voltage measurement such as temperature and current. But this does not necessarily take into that the battery has been subject to abuse from out of tolerance voltages, currents or temperatures which leads to reduce the life of your battery. Apr 7, 2016 at 9:50
• @codo when the battery is sick, do I still get te same battery voltage at full charge as when the battery is new?? example : 4.2 volt???? Apr 7, 2016 at 10:02
• The discharge time is depending on the used conditions of the battery. The battery can has a poor health in case of increase of the internal resistance which leads to reduce the charge time and not the discharge time! Apr 7, 2016 at 10:03
• @MakhloufGharbi -Yes, you will still get the exact same cell voltages from the battery when it is new and when it is at 50% or 80% life left. Cell voltage Will only change when the cell is damaged beyond repair, but that will also be obvious. There simply is no way to measure state of health of a battery using only voltage. I wish there was. Apr 7, 2016 at 21:46