Technical Fpr replacement car won't start

[Bravo dynamic 120hp]

Fiat bravo 1.6 multijet had codes
P0091
P0092
Replaced fuel pressure regulator with Bosch one and car will start for one second and cut out put old one back on and car starts no issues anyone any ideas as I don't know what to do with this car anymore

 

[Mike1alike]

Start with checking the battery. Discharged battery gives you those symptoms.

 

[Bravo dynamic 120hp]

What's the best steps to checking it I am somewhat mechanical minded so can only do so much

 

[Mike1alike]

Hello, sorry for not replying earlier.
Best way to check the battery is probably reading it using a special battery tester that shows you the battery's voltage, state of charge, state of health, internal resistance, the amount of stored current. If you don't have a tester you can have it read in a garage or a shop that sells batteries.
Without the tester, a reading of the voltage using a multimeter is pretty useful. You have to read it in the morning, before starting the engine. Voltage above 12.5 V indicates good and charged battery, below 12.0 V indicates discharged battery.
How is the car? Did you fixed it?