just takin a stab here...
if your magneto,or coil or ignitor are, one or all faulty your bike would try to fire off battery and then have a weak spark.. " to check charging output.....
once the new battery is hooked up start bike turn high beam on, and set your multi meter to dc volts read across the battey (red to red black to black)output should read14- 15.5 volts dc @ 5000 rpm...edited from susuki service manual.".good luck!!