If your engine is starting fine till 40% N1, the battery should be ok.
Start derichment isn't relevant, fuel derichment takes place between 25-40% on this engine.
Acceleration adjustment is relevant. Your engine maybe 25 hrs TSN, but how old is the fuel control unit?
If it is a CECO system, there are two 'Max Pc stop' settings, '+' and '-'. It is basically an acceleration fuel flow setting. This is normally set before the fuel control unit is fitted to the engine and depends on what aircraft type the engine is fitted to. Just a thought, and might be worth checking if a dirty compressor, faulty fuel nozzle, sticking bleed valve aren't the problem.
Probably telling you something that you already know, but this engine prefers to be started hot and quick (in limits of course).