sounds like you have more issues than you think. I would start with the A/C side where it goes into the converter and make sure that has power. then the output of the converter for 12V power. then I wold start looking for what I suspect is a good short thats sucking all the power away. take the LiFePO4 battery to a different charger and charge it and leave it out untill you find out whats going on. realy this is two hard for someone to tell you somthing spicific, so you going to have to check every wire for mouse dammage and that is every bit of it till you find some dammage, fix it, test again, if its still screwwed look for more dammage.. might get luckey, might take forever..... sorry I can't be more help but what ever is going on is what killed your previous batteries.
