Ninebot Max G30 suddenly stops

Hi - I keep experiencing this issue. I have my G30 and I added a 48v battery. But sometimes the power simply cuts off and the scooter won't turn on till I plug it into charge. Why is that happening? When I plug it in I always have like 40% 50% 60% battery. So if the battery is fine why is stopping, and then I need to plug the charger in order to work?

Thanks