It is important to know if you are measuring the battery after charging it from a source off the bike before checking the charging system.
A lead acid starting battery can be charged safely to 14.5V. But at that point the charging rate should be reduced. A battery charged and then rested for two hours should stabilize at the 12.6V to 12.8V range.
When on the bike, it matters at what RPM the charge voltage is measured, as the alternator output falls to about 1/3 of max at idle vs. full output at 5000 RPM.
Technically measuring 13V at the battery means it is not depleting, even if not accepting charge very fast. Our bikes do normally deplete the battery at idle speed and then recharge it while driving about. This makes the battery voltage variable depending on what state the battery is in at the time of measurement and the speed of the alternator RPM.
Automotive charging systems provide ALL the power needed to operate the machines and usually do charge at idle as well as higher RPMs, and maintain the battery at right around 13.8V. The battery is generally needed only when operating the starter motor.
Stock SOHC4 need the battery to keep spark alive during idle.
Know that the battery charge state dominates the voltage measurement, NOT the charging system. For example, if the battery were totally depleted, the voltage would be about 10V. The charging system should raise that voltage. But, it will do so slowly. It may well reach the peak of 14.5V, but it could take 10 hours at 5000RPM to fully restore the battery to full status.
So, measuring the absolute instantaneous battery voltage, does not take into account the transitional nature of this bike's electrical system, or which way the system is trending up or down. 13V could be a way point on its way to a higher voltage, or a way point on its way to a lower voltage. And the trend information is important to know as well as the current operating condition.
If you toss a ball from one hand to another, it travels in an altitudinal arc. Stating the current altitude in transition does not tell you if it ascending or descending or if it has reached the apex of the arc.