However if the battery charger is not recharging the battery then the problem is beyond a bad red LED lamp and is more likely to be a faulty battery charger. The problem could also be a faulty battery charger port which has a short circuit.
Both the battery charger and charger port could be replaced at the same time to avoid testing, or the charger's output Voltage could be tested to see if it is working or not, and the charger port could be inspected to see if it has any visible problems.
We sell battery chargers and charger ports for Hoverboards on this page: http://electricscooterparts.com/self-balancing-scooter-parts.html
Please let us know if you have any questions.
I would say the charger is faulty.