Kindly elaborate "sometimes when driving" when doesnt it work ?
and Yes Mira has one battery for the car and the eco idle so it requires a 50Amp battery of special type which is not available so everyone is forced to get a simple 50amp battery
Other than that Mira has CVT and CVT fluid has many types so consult manual and buy the correct CVT type and the amount to put in.
For CVT fluid dont just pull the drain plug and change the fluid its useless a complete flush is required so open the CVT fluid pan and clean the filter and then attatch it again and fill the new CVT fluid.
The fluid that comes out will be less than the amount to put in as in user manual that is completely normal since some of it always present in the gearbox it self