[Skuzzy]

Excaliber, notice I said "fully charged" and "not connected to the electrical system".

Yes, if you were getting 15V out of the regulator, your regulator had stopped regulating.

It does not hurt to disconnect a battery for the winter. It usually is a good idea to trickle charge them once a month while they are not being used though. That is not to say the battery will die if it is not done. I am just saying it is a good idea. Definately will not hurt.

Then again, it also depends on what the battery design is. Some battery designs are more immune to breakdown.