have you made sure the wiring on the mod is in series (or parallel) depending on how the egg runs (i cant remember) if it runs on 9v then you must pair both red wires together when you solder to the board .but if it runs on 18v you must pair 1 red to 1 black and then solder the other black to the negative (-) on the board and the remaining red to the positive (+) on the board ...if you are running the board at 9 volts when it should be 18v you will get a constant low battery warning ..which is probably your problem..as as far as i can remember eggys run at 18v
EDIT ..of course i could be completely wrong as im a bit pissed and seeing as you have attempted the mod in the first place you probably know this.....so ...eh....IGMC