2004 Ford Taurus 27k miles and a mess

Electrical problem
2004 Ford Taurus 6 cyl Front Wheel Drive Automatic

about 2 yrs ago battery wouldn't charge, work from home so not driving alot. Replaced battery and that worked for a few months bad fuel cell? And replaced bat. Lasted few months then car would have to be driven every4 days to keep running. Symptoms were turn key hard start or start and all running lites on dash were there and wouldn't go out. Turn off and restart lites went out, sometimes it would give poof sound on start. Took it in to local and he said a parasitic wiring prob. Needed a smart junction box?As he had traced the wires and said it was fuse 37 I think? As it needed to be programed I went to ford and they put in this smart box and reprogrammed that was mar 31 car ran fine till this am as it seemed to ride rough
died in shopping center and a guy jumped me and said u need gas, car had 3/4 tank when I drove 2 miles it store not the gauge said 13 miles to empty when to gas station got 15.00 (47.00 to fill) then GG read full? Drove 15 mins to try and charge bat came home and was sitting in drive and had food on break was in park and watching this same gauge going down 244, 241, 239 took foot off break it stopped put foot back on and it started down again.
my? Is what is the real problem? Does this smart box with fuses control this gas read out on the dash?
no computer lites on dash ever come on to say what the problem is. Had fords for yrs and on our other one only needed to replace the oxygen thing once but I am ill about this new car as I don't want to keep putting bucks into something that isn't gonna run or I have to drive every other day, thanks