What is the purpose of checking the open-circuit voltage of a motorcycle battery, and what resting voltage indicates a fully charged 12V AGM battery?

1. It measures the battery's state of charge without any electrical load; a fully charged battery should read 12.6V to 12.8V or higher.
2. It measures the charging output of the alternator; a fully charged battery should read 14.5V.
3. It measures the internal acid resistance; a fully charged battery should read exactly 10.0V.
4. It measures starter motor current draw; a fully charged battery should read 0.0V.