16V on a car is bad. 15 - 15.5V on anything is bad.
You should be looking at around 14.4V but not less than 14 at 5krpm. And definitely no more than 15.5V at 5krpm, if its doing over that at idle you have a big problem on your hands if you don't take care of it.
Anything over around the 15 - 15.5V range will be overcharging the battery which causes an excess of hydrogen gas to be released, and even the electrolyte in the battery may boil...
If you mix the hydrogen with a spark you wont be having a good day. That is why when you read the user manual that came with your battery charger it will say only charge in a well ventilated area and not in the vehicle.
If the electrolyte boils it can spew sulphuric acid all over the inside of the bike around the battery as it vents through the pressure relief valve, again - bad day. Not as bad as when the relief valve is blocked though cause then the battery can explode....
Beginning to get the idea mate?
Running the battery to over 15.5V for short periods of time is perfectly safe though as the battery doesn't get the chance to overheat, the main risk you are looking at in this case is to the electronics in the bike, but it will take more than that to fry them... and the fuse should blow before it gets to the damage point.