NO. The properties and characteristics of CNG and LPG are different. The safety relief valves and other devices are set for a particular pressure of LPG. There is no fill limiter in case of CNG tanks as it meant for the Services of Gas. The fill connections are also different for LPG and CNG. Hence, not advisable to use CNG kits for LPG Service.
Maruti Alto 800 has a tank capacity of 35 litre, to know that how much petrol is left in the tank, divide 35 with the total no. of bars say 10, then if the fuel gauge indicates 2 bars it means there is 7 litres fuel left in your tank.
The 2-year warranty is for the engine and transmission box while other components like tyres and battery are come under respective manufacturers' warranty. Like if you have Exide battery, the warranty claim will be handled by Exide not Maruti Suzuki, the dealer must have provided you the warranty card at the time of purchase.
To say that the new Alto 800 is not upto the mark of the old Alto Lxi is not true. The new Alto 800 is a more refined car than the old version. Also Maruti has worked very hard to make the steering more agile. It also looks more pretty. But, if you want an Alto that is more agile and spunky, you can go for the Alto K10. The K10 is also a very good car and is very nimble. The Alto range is very reliable and brilliant city cars.