Battery voltage question

Another Update.. so I decided to go for another ride earlier today.. on initial start up I put the volt meter on battery and it is reading 15.30 volts ( no accessories on).. seeing I had the kids and wife ready for a little ride I went anyway..
My ammeter reading was pretty much in middle of gauge the whole ride.. I get home and put the volt meter on battery again and it's down to 13 volts.. I'm going to hook up a volt gauge (in car) to keep a closer eye on it , but is this normal?
Thanks in advance