Dear, the first problem which you faced was due to CNG fuse failure in Engine bay and the passer by person directed the connection. Its good you went for relay installation only as there is no issue in your CNG switch.
Blinking of battery light is can occur due to,
1- Loose connection at battery.
2- Electrolysis depostion (Greenish White) on battery terminals
3- Generator Failure.
For serial#1 & 2 it will blink only whereas for 3 it will light up continuosly.
I suggest you to remove the terminal wires, clean terminals with sand paper & later hot water. Connect wires tightly & drop 2-3 drops of clean lube oil on each terminal. Then check it hopefully it will work.
Even if it persist don't directly go for Generator repair as there can be loose connections some other points like fuse etc. Then refer some good electrician to test the Generator with Meter.