CX3 battery problems

[Oobers]

Hello. I am a new member on this site and hope someone can help me with a problem I am having. I have a CX3 2017 model, petrol engine. I have been away for 10 months and on returning the battery on the car was dead, which was no real surprise. I bought a Schumacher SC1339 trickle charger/conditioner and put it on the battery in the car, and the lights indicated that the battery was sulfated. After about 7 hours the lights on the charger turned green indicating that charging was complete but I left the charger on over night to be sure. The next day the car was totally un responsive, so I jumped started it from my wife's car and was going to take it for a long drive to charge up the battery. But the power steering kept switching off and the engine cut out. After another jump start to put the car back on the drive I noticed that there was an error message saying that the engine management was malfunctioning, as well as the istop. I have ordered a new battery, and I am hoping that I haven't buggered up the computers on the car. Time will tell I guess, but has anyone got any thoughts on the matter?