"Invalid Battery" shuts down phone

    My G4 came with 2 batteries which I switch around every month or so, using the other as a spare. (Both genuine LG batteries)  Prior to my last switch attempt, there was an Android update for the G4 and ever since then the only battery which works is the one in the phone during the update.  If I install the other battery, the phone boots ok, runs for about 30 seconds, reports 100% charge, and then shuts down after a brief "Invalid Battery" message.  This is bad!  Does anyone have any idea what's going on here?

     

    I've tried the following:

    1: Cleaned the contacts to make sure all four connect well.

    2: Checked that none of the contacts are bent.

    3: Cleared the cache.

    4: Many, many reboots.  The problem follows the battery.

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