This cheap DIY Induction Heater kit is ideal to learn about induction heating. The manufacturer boasts that this little module can handle 150W at 12V though the power supply must be able to supply at least 5A at a minimum. Hence, do not use these induction heaters with normal batteries but use a suitable power supply to ensure proper functionality.

At Leobot Electronics we have a range of other induction heaters available but this is the smallest and cheapest available.