It's probably not the batterry.
1- 15 volts and more when you hit the buton you are good to start it.
2- look for good blue spark at igniter for 10 sec.
3- Look for good spray pattern at the start fuel nozzle when you remove it and simulate a start. ( check for proper shimming
4- Might be the start drain valve that leak fuel back to tank.
5- Might be clogged start electrovalve.
6- might be pressurizing valve( remove the be nut and look for fuel with boost pump, if their is you have a problem.
7- Bad FCU
I when throught that last month and it was a bad FCU.