My Suzuki Gn 125 motorcycle does not start

For a few days I was presenting problems, I had to move the helm so that the motorcycle start could serve me, but 2 days ago the battery stayed without a load tried to start it running and this encazio, but when when he turned on this he stated, not the sound of the engine was not stable and when he stopped accelerating, he went out, the mechanic told me that the battery no longer served, I bought a new one. Normally, and again the battery was discharged only that this time the battery was new, and my motorcycle is still unlocked.

What should this be due ??????

If the batteries are discharged I check the burden of the alternator or current generator, to know if it is feeding that to eat.