Interesting Charging Dilemna

[xj550]

Hello. I'm at a loss with my charging system. I have an xj550rh Seca. When I hook my multimeter to the battery terminals and rev it up to 3000rpms the volt meter reads 14.5 volts. Great, right? Okay, the problem is that after 20 minutes of riding it no longer has that same reading. So, after a ride of about 20 minutes I'll go home and hook up the multimeter to the battery terminals again and rev the engine to 3000rpms and it only reads 12.5 to maybe 13 volts. Is this suppose to be happening?

[R]

Is this actually causing a problem though ?
Could be the 'trics are sensing the battery is charged, and cutting back on the charging rate.

But, if you ride around at night, do the lights fade away to a dim glim.
Measuring the battery voltage before and after a ride may give more a hint of what is happening,
without the danger of becoming a dark motionless object on a black night !!.

[xj550]

To be honest, no it hasn't been a real problem. I'm just curious why it does that. I can't find any literature that explains this.

[xj550]

I also can't say the battery is fully charged when I get back home. I just make it a habit to put the charger on every night but the battery is definitely not fully charged. I've read that the charging systems on these early eighties Japanese bikes are at best pretty bad so I'll just let it go.