i have noticed that my hi power screamer fan which cools me motor , slows down when i apply fully throttle on 4s , so thats them packs knackered then , i plug into the balance lead , its a great way to check the batts in use . i found a part used 6s pack in my garage and put that in . couldnt touch full throttle as didnt want to blow my badlands , some huge slides done and cooked another motor , the lawn does that , lovely jubby