Sounds like the battery.
Voltage isnt really an indication of a good battery.,
I had a van that was slow to turn over like this for weeks, was only on a morning, rest of day fine.
Battery ended up being replaced, go get it tested
Other than that it could be all manner of electrical faults, bad earths, alternator, ignition switch, the list goes on, but i would bet its the battery and its the first place to start.