Greetings gedemeisterdk,
A high proportion of model aircraft fliers have changed from using NimH to Lipoly batteries.
Many of these now obsolete chargers are capable of charging up to 24V.
Most require a powerful 12V DC power supply but there are internet sites that show how to convert an old Personal Computer PSU to this purpose.
Alternatively search eBay for 'scooter charger' from £ 17 delivered.
Dave