Blog / How to estimate the remaining capacity?


When data is acquired correctly and consistently, internal impedance has been shown to have a strong correlation with capacitance, and while it is not a direct measure of capacity, it can be used as a battery health indicator to predict residual lifetime. An increase of 25% indicates a decrease in performance from 100% to about 80%, so a 25-35% increase in internal resistance will be acceptable, with a standard replacement schedule.

Between 35-50% increase of the Internal Impedancewe have a clear physical signal on the degradation of the battery capacity which therefore approaches the end of its life cycle. Exact lifetime is almost impossible to measure. However, to ease estimating how long can the battery still provide reliable functionality, some Adelsystem CBI devices work out the effective capacity of the battery based on repeated charging and discharging cycles. This sophisticated algorithm unobtrusively works while the CBI is performing its activity and provides an indication of the actual remaining capacity, expressed in ampère-hours.

Such figure is compensated for variations in battery temperature, load current and charging current. It is compared against the user-defined nominal battery capacity and consolidated with the measured battery internal impedance time-evolution in order to yield the percent state-of-health (acronym SoH) of the battery. The percent SoH can be conveniently read from the device using the DPY351 connected through the AdelBus, which ensures optimum at-a-glance monitoring of all the battery characterizing parameters so that everything is under control and preventive maintenance can be implemented thus averting equipment or production downtime.