If you are sure that the battery is good, but the starter motor is too slow, you may have corrosion in the starting system. Do a very thorough check of all your connections. Start at the battery and check the main terminals, and scrape off any rust or corrosion you may find. Check the battery ground, and then the other end of the battery positive, where it connects to the starter solenoid. Check the connection down at the starter motor. Check the starter ground, but usually the starter has a really solid ground.
Remember too that each time you hit the button and make the starter motor turn over, you are wearing down the battery. So if you check a connection, and then test the button, check a connection, test a button, etc, you may find the source of the problem way down the line, but by this time the battery is too weak to start the bike. Conserve your battery life, especially if you are somewhere remote.