I have two Razor mx350 dirt bikes. Both ran fine up until recently. They both had new batteries that were only a couple months old. All of a sudden they stopped charging. I thought the batteries had crapped out, so I replaced them. I also replaced all the electrical on one and the charger port on the other. Both worked great until I charged them and the batteries died again. This has to be a charger problem right? I tested them with a multimeter and it shows 28.2v. Any ideas.