Hyundai I45 2013 Problems

Check for possible damage that might have been done by those who 'borrowed' your car. It's possible that the battery is completely dead, but I think that's unlikely. Take it to a Hyundai dealer and have them try to find the cause of the problem.

You are likely to get a little better fuel consumption and perhaps better performance, but you need to measure that against the higher cost of premium to determine if the improvements are worthwhile.