old Xantrex (now conext) XW6048 with LiFePO4 batteries

I have some old LiFePO4 batteries from a cell tower backup I got at the junkyard. I need new batteries for my system and do not want lead acid batteries. I thought I would put a BMS on these LiFePO4 batteries and try them with my inverter before I bought new LiFePO4 rack batteries. I can't get them to work. I think the BMS  cuts the power to them when they are charged. I get error messages no matter what i try . Is there a way to use LiFePO4 batteries with this inverter? If the batteries are charged the solar will run for a while but then shuts off with error messages. Its been awhile since I tried them and don't remember what the error messages were. Any Ideas? Thanks.