Quick answer
Malaysia's Road Charge is RM20 per entry for a foreign-registered private vehicle. It is separate from Malaysia VEP registration and from highway tolls. JPJ says motorcycles and commercial vehicles are exempt from the Road Charge.
Road Charge, VEP and tolls are different
The Road Charge is an entry charge collected by Malaysia. VEP is the vehicle registration system for foreign vehicles entering Malaysia. A toll is charged for using a particular road or crossing. Budget for each applicable item rather than assuming the RM20 pays for the full drive to JB.
How to prepare to pay
JPJ's FAQ says the charge can be paid using a Touch 'n Go card or a Touch 'n Go eWallet linked to the VEP RFID tag. Check the balance and the vehicle's VEP status before travel. If a payment method or enforcement procedure changes, JPJ's official FAQ and VEP portal should take precedence over this guide.
Example for a return trip
A Singapore-registered private car entering Malaysia once on Friday and returning to Singapore on Sunday has one Malaysia entry for Road Charge purposes. If it leaves Malaysia and enters again later, that is another entry. Actual tolls and other costs depend on the route and vehicle.