How do i charge a battery on a honda fmx650? where are the terminals?

Sounds like you have a bad battery. The batteries usually are done when the fail, it may take a charge but not hold it.

Remove the wires from the ATV. Clean the terminals..wire brush.. Charge slowly.. about 2 amps is max... like BBQ.. low and slow!

Now clean ALL the wires that attach to the battery. Use a stiff wire brush or fine cut file(what I use), then GREASE the wire ends and battery terminals when you reassemble. I little goes a long way. I like the terminal spray that Wal-Mart sells along with the terminal felt washers (small black spray can)

It could be your battery. It could also be your alternator, or just corrosion on the battery terminals. I would remove the battery and clean the terminals. Take your battery to a auto parts store. Most will check your battery for free. If your battery is not charged fully ( which is likely) they will have to charge it before testing. This could take a while. If the battery checks out get some battery terminal grease before you leave the store. Reinstall the battery using the grease. Drive the car up to the store and ask to have the charging system checked.
If you can get the car started. This entire procedure can be done at the store. But you would be running the risk of the car quitting on you somewhere on the way to the store.

Clean your battery terminals and charge your battery. Or clean terminals and get a jump start. Your battery or alternator may be going bad.

change the battery cables terminals you can get them at walmart for under 5 bucks last time I checked

Hi and welcome to FixYa,

Offhand, it would appear that the charging circuitry has failed.  Initially, check the rectifier/regulator combo and its connectors/terminals.  The regulator is located behind and below the coolant reservoir. Check for any loose, burned or corroded terminals:

• 3 yellow wires from stator;
  
• green wire to ground; and
  
• red/white wire from regulator to starter relay (to battery - charging line).
  

The voltage on the the red/white wire or the battery + terminal should rise from 12 + to 14+ as the engine RPM is increased.

Good luck and thank you for asking FixYa.