had this before on a 48volt hyster, drove me crazy becuase there was no problems with the unit.
check what your battery voltage is dropping to while accelerating.
i bet you installed a multi-voltage back up alarm and it see's the voltage drop to threshold and changes state to 36v from 48v or 24v from 36v.
my fix was install an alarm just for 48volts, let me know how you make out.
This is ONLY to be used to report flooding, spam, advertising and problematic (harassing, abusive or crude) posts.