Brother Baleno is most pathetic due to electrical issues specially on CNG.
Firstly use a single genuine OEM gasket.
Check all the valve seals and tappet seals for leakage of engine oil and gear oil
Service / Replace the radiator and flanges (metal pipes which go to engine for water) and rubber pipes. If there is no leakage in the system the water / coolant will remain constant in the car for months.
Use thermostat and auto fan once all the radiator and fans are in proper working condition.
Always use a high quality coolant like Toyota SLLC or ZIC Coolant.
Now coming towards the electrical part you will need to change the 4 ignition coils and starter motor for your car from kabar market.
In excellent condition it will cost you Rs. 1,000 / coil and Rs. 2,000 for starter motor which will easily work for 2-3 years in CNG cars.
Check the ECU for errors on any OBD scanner.
Check all fuses are in proper place and wiring is properly done with no cutting or short wiring.
Also check the Alternator and Battery with multimeter for voltage. It should be more than 12V for Alternator.
Check the car when engine is running at night, the places where current is leaking will glow like stars at dark. DONT touch anything its high voltage.