Road distance from Ernakulam to Wayanad (Kalpetta) is about 240km.
So it's Ernakulam --180km--> Calicut --60km--> Wayanad (Kalpetta).
Ernakulam to Sultan Battery (270km): Ernakulam --180km--> Calicut — 15km –> Kunnamangalam — 30km –> Thamarassery — 15km –> Adivaram — 12 km (Ghat section) –> Lakkidi — 5km –> Vythiri — 6km –> Kalpetta — 8km –> Kainatty — 23km –> Sultan Battery
For reaching Wayanad by train from Ernakulam, take one of those northbound trains to Calicut. From Calicut take a taxi or bus.
The best public means to travel from Ernakulam to wayanad is by bus.
There are a reasonable number of long distance direct buses from Ernakulam to Manandavadi and Sultan Battery. Those Mysore bound KSRTC buses (both Kerala's & Karnataka's) goes via Mananthavadi and Sultan Battery in Wayanad.
You can even do advance seat reservations (www.ksrtc.in)