Hello MiaLuo,
The Bpod State Machine does not have a battery, and does not need to be charged. It derives its power from its USB connection to the PC. State Machine r2, r2.5 and r2+ derive power for the solenoid valve driver from a separate wall adapter.
Which state machine model do you have (e.g. r1, r2, r2.5, r2+)?
What are the specs on the charger you're using (e.g. 5VDC 1000mA with USB connector or Barrel Jack / positive center)
Thanks,
-Josh