SLUUCP8 June 2024 BQ41Z50
The BQ41Z50 implements a new state-of-health (SOH) function. Previously, the SOH of a battery was typically represented by the actual runtime FullChargeCapacity/Design Capacity (or FCC/DC). Using the runtime FCC, however, is not an adequate representation for the state-of-health, because the runtime FCC reflects the usable capacity under load. A high current load reduces the runtime FCC. If using just the FCC/DC calculation for SOH, the SOH under high load will be worse than the SOH under typical load. However, a smaller usable capacity at high load does not mean the SOH of a battery is degraded. This is the same when FCC is reduced at a lower temperature.
The BQ41Z50 implementation of state-of-health addresses these issues. It provides the SOH of the battery through an SBS command, SOH(). The SOH() is calculated using the FCC simulated at 25°C at Rec Temp Charging:Voltage with current specified by SOH Load Rate. The SOH Load Rate can be set to the typical current of the application, and it is specified in hour-rate (that is, Design Capacity/SOH Load Rate will be the current used for the SOH simulation). Separate thermal model temperature factor SOH Temp k and thermal model temperature SOH Temp a are used for SOH simulation. SOH Load Rate, SOH Temp k and SOH Temp a data flash settings are used for SOH() calculation only. This SOH FCC is updated at the same time ASOC and RSOC are updated. Since this implementation removes the variation of current, temperature or voltage, it is a better representation of a battery’s state-of-health. The SOH FCC is available on MAC StateOfHealth(). SOH FCC is initialized with lifetime Min FCC-SOH until SOH simulation is completed on POR.