65 Ammeter now shows overcharge when accelerated

The normal ammeter indications will be C (charging) to some degree when the battery is discharged any amount, as noted. If you drive long enough, the C indication will gradually diminish as the battery charges.

So, the ammeter indications will vary for normal operation; that can be confusing. If you turn on the lights after having driven for a while and the battery is well charged, then it would also be normal for the ammeter to show a slight D (discharge) indication as the system 'settles in' to a lower operating voltage, and the battery discharges bit to reach that lower voltage.