On the series 2 it's not an issue at all.

I believe David Smith, the developer of Sleep++, said that on the original Apple Watch he wore it all day and all night and simply charged it in the morning and in the evening while taking a shower or doing the dishes or something like that. It doesn't take that long to charge the thing up all the way, so two short charges while you're doing other things would be enough to top it off.

On the series 2 the battery life is so good that just charging it while you take a shower in the morning is probably more than enough.