Well this was easy. Im surpised no ones done this yet and made a mod of it. I can't say this is accurate, but it is playable without setting the boats battery recharge rate in the basic.cfg file to 1000 and making it a freaking nuclear submarine. (most common fix ive seen for this)
Heres what i adjusted:
Surface propulsion:
-max speed 18.3 (probably unneccssary, unrealistc, but what the hell)
-Engine power changed from 4400 to 4500
- Engine RPM chnaged from 520 to 550
Now for the important part:
Submerged Engine power

HP) Changed from 5000 to 2500.
With the above tweaks in the sim file, the sub recharges just like an IX boat. All i have to do now is look at the boats duration at a given speed.
Might be the start of my own mod :hmm:
I have alot of other things im doing in conjunction to this to make the game more challenging in what is an unrealistic, but fun boat.
Such as.. well found out why going deep was so helpful.. AI can only detect you down to 300 meters. So if your diving deeper then that, well, your pretty safe. Thats changed in my game