Have you done basic check's, are the battery cables tight, is the negative cable tight wear it's bolted to the bike.
When you say you've checked the battery don't forget that it may be showing correctly when fully charged but as soon as you put it under load it may show a problem like a dead sell ..
I had a similar problem with one of my bike's mine was reluctant to start head light dimming dash lights dimming, I thought it was the battery fitted new one still the same. It turned out to be the starter motor brushes not making a good contact a couple of minutes with a round file did the trick & 25,000 miles later still OK.
Ian.