Voltage Drop When Starting

Have a 2001 250 Evinrude, no problems starting it, cold or warm, until now. Manual says voltage cannot drop below 9.5 when cranking. Mine drops to 8.5 when cranking so the computer is probably not getting enough juice. However when I turn the key one click, to get the diagnostic lights, the voltage registers 13, normal. I put in a new battery in early July and that's the one I've been using. Yesterday I replaced the other one so I have two new batteries. Switch set to both or just the brand new one doesn't change a thing. Starter is new this year.

This started on the last start of the day Labor day (finally got it to go) and yesterday when I went to start it. Previously it's been flawless. What could suddenly account for this?

Thanks in advance...

Here is a link about doing a voltage drop test that should help you diagnose your starting problem

http://www.excelauto.com/online/Tech.d/strvdt.html

Check the Cable from the selenoid to the the starter. I had this on my DI, and it looked perfect at the ends, and the inside was very corroded under the PVC jacket. When wet it worked like a charm, when dry, it killed the cranking battery with a huge voltage drop. Easy fix if that is the prob.