The only thing the rom can (maybe) control is the currency that will go to the battery. And for that they would need to install a resistor to do just that (for which i doubt) to decrease the currency to less than 1000mAmps that the charger outputs.
The battery controls the charging, not the phone. The only thing the phone does, is show the battery left, (not very accurately indeed), and use the power needed.
In my phone I thought battery drained fast with new rom, but I'm not sure now.
Charge it with it's own charger since it's a rather big one (1000) and not some other which is probably weaker (most are about 250-500 mAmps).
Let it drain completely for a week and then fully charge it, and don't connect it to cable in between because you can't get correct stats.
Sent from my ZP980 using xda app-developers app