Car electrical issue

So I got a 2012 ford focus se 2.0 liter engine size and I’m having issue with the electrical part. First what happened was my ecm was damaged so I had to order a new one(from flagship one) when I had put it in I had got a locksmith for the passive anti theft and key reprogrammed. Come to find out my battery was dead so I had to get it replaced and once I did my car still wouldn’t start so I took to an electrical mechanic and he told me that the ecm wasn’t programmed with my vin number. So I had to ship it back to flagship one and told them that they didn’t programmed my ecm to my vin number so I waited for like a week and then I got it put it in and had a locksmith do the same procedure and he had told me my battery was off because when I start the car the lights kept flicking off and on.

So I don’t know if the problem is the battery or something else please help😢