Lawn mower not charging the battery when running

Hi guys
    Can anyone help me out with this. I am wondering if these yamahas have a charging system and how they function. The battery runs down to 10 volts presently when running because of the electric fuel pump and the electric PTO. The PTO barely wants to turn on probably because the voltage is too low. How does the battery maintain 12+ volts and how can I look to repair the charging system. Obviously there is a generator or alternator I assume somewhere but I dont see an external one. Thank you for any help anyone can assist me with. I greatly appreciate it! Paul