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BQ34110: SOH always reports the same info regardless of battery state

Mark Scovel
Intellectual 595 points
Part Number: BQ34110

Below is the SOH info from the TRM.

We are polling the bq for SOH every few seconds (among other data). No matter what state the battery is in, SOH always reports the same thing: capacity=100, energy=8400

What are we doing wrong?

StateofHealth(): 0x2E/0x2F
This command returns the state-of-health (SOH) information of the battery. StateOfHealth() is calculated
as a percentage of FullChargeCapacity() relative to Design Capacity. It is a read-only command.
Byte 0: LSB of SOH in capacity
Byte 1: MSB of SOH in capacity
Byte 2: LSB of SOH in energy
Byte 3: MSB of SOH in energy

  • 0
    TI__Mastermind 25955 points
    Hi Mark,

    Has FullChargeCapacity() for your device changed? Design Capacity remains constant. If FCC has not changed, there should not be a change in SOH.

    Sincerely,
    Bryan Kahler
  • 0 in reply to Bryan Kahler
    Intellectual 595 points

    Well what does the 8400 mean? 8400/1300 mAh (our design capacity) = 6.46 so I don't know what that number signifies.

  • 0 in reply to Mark Scovel
    TI__Genius 14985 points
    SOH is a percentage and is expected to change very infrequently. It represents the health of the battery compared to when it was new. It will only update when Qmax or learned resistance (Ra) changes. It does not depend on whether your battery is full or empty nor on the present temperature. It also doesn't depend on how the battery is currently being loaded. The gauge calculates SOH by running an FCC simulation at a fixed temperature (25degC) and a fixed load (customizable in dataflash through the "SOH Load I" parameter from Table 11).

    Per the datasheet:
    7.3.2.10 StateOfHealth(): 0x2E/0x2F
    This read-only command pair returns an unsigned integer value, expressed as a percentage of the ratio of
    predicted FCC (25°C, SOH current rate) over the DesignCapacity(). The FCC (25°C, SOH current rate) is the
    calculated full charge capacity at 25°C and the SOH current rate that is specified in the data flash (State of
    Health Load). The range of the returned SOH percentage is 0x00 to 0x64, indicating 0% to 100%,
    correspondingly.