1st gen and series 1 are not the same watch... series 1 is a little bit better. That said, for my series 2 on beta 2, the battery doesn’t last a full day like it did on watchOS 3
Oh, sorry, I got the 1st Gen and Series 1 confused. I have the Series 1, you have the very first original Apple Watch.
I would think the Series 2's battery life won't be as good as my Series 1 because 2 has built-in GPS. Can you turn it off and only use it when you go for a run or whatever?