Is it making more noise than usual? Could be that the motor is partially shorted and is overheating.
Low cost pile 'em high and sell 'em cheap items generally have next to no spares support. Consider ditching it and treating yourself to a new one. Maybe an Eindhell cordless - Eindhell do seem to support their kit.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix hedge trimmers.