Secondary Battery Charging Issue - 2006 Mercedes-Benz E55 AMG 5.5L Supercharged

I was contacted from a local shop Ultra Performance in Winder, GA  to test out a Secondary battery charge code issue. It was a race week but wanted to get this car done for his customer so he dropped off the vehicle to CLG Performance to test wiring. The basic checks were done at his shop so they gave a run down of what was going on. The secondary battery wouldn't charge. The relay could be jumped to charge the new secondary battery but he needed me to find out what was going on while he was prepping for the races. I got a wire diagram of the vehicle and started hunting following the wiring from the secondary battery to all the modules it connects to. First I checked the heavy duty relay was switching using a scantool and it would work but you didnt see the voltage of the battery on the scantool. I hunted more and disconnected all the batteries and put on a wire trace on the power wire of the secondary battery connection. I then searched the entire car as this was the first time dealing with this issue. It finally led me to the trunk area. thats where I found a corroded terminal in a connector, no sign of water coming into the trunk anywhere which was weird. Here is what I found..
 

This was the culprit module
 

I opened to see if I could repair and I was able to replace the 2 pins that were corroded away. It was very difficult as you have to melt plastic and pull the original pin out. Luckly it was an edge pin so I had room.


I was able to get new pins in that I got from a junk ECU that was long enough to shape it the way I needed it and solder in new plastic from a drilled hole and got new pins made (very difficult to do) But it worked and I was able to see the secondary battery voltage with the scantool after getting everything hooked back up. I took some Liquid Tape and sprayed the back of the connector to fill where any water could travel since the factory connection has no insulating pins inside it. The liquid tape filled the area good to prevent any further water damage. Job was fixed and sent back next day. So if anyone has secondary battery codes, look in the trunk for this module as this may be the culprit