Get a sealed AGM battery if you can that fits... Its going to cost a bit more, but then your not dealing with a flooded lead acid battery anymore. The AGM have better cranking power and last longer as well. I went through two old the traditional batteries before i bought the AGM i put in my 200ES, man was that a worthwhile upgrade!! I had the same problem as you, not enough cranking power after sitting and then it would be ok after it ran a while.
I hear now they are making Lithium Ion batteries for Motorcycles, the cranking power is amazing with them. If they ever make one close enough to the right size i will get one for my 200ES... I have Lithium batteries in just about everything now, what a world of difference, slow self discharge and super power output.
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1984 Honda ATC200ES "Big Red"
1982 ATC200E "Hondie"
1988 TRX300FW "Project Quad" Still in progress....