The city I live is located on top of a hill/low mountain. When I drive uphill by following speed limits to my home the car often can't keep recommended speed (45 mph). The speed drops significantly(can go even 25 mph) and unpredictable. At the beginning I believe the car was able to keep the speed but it slowly started losing the power. The risk is that a vehicle behind might not expect such behavior from my car and also changing lanes is tricky because it can't accelerate and it moves slower than other cars on the road. I've contacted dealership's service two times but they didn't find any issue. I also contacted Hyundai's customer support but they wasn't able to help me as well. The person from the service said that Hyundai is aware of the situation but they don't have any solution. My guess is that the problem is with battery. Battery performs as buffer to power electric engine in hydrogen fueled vehicles. When I drive uphill the battery probably drains fast and the energy from hydrogen can't charge the battery on time. The car doesn't show any warning lamps or malfunction signs on dashboard. I'm ready to cooperate with vehicle inspection if needed.

- Rancho Palos Verdes, CA, USA