1 Series Battery Issues (help needed pls)

[owen0510]

A family members 2009 1 series is cranking when trying to start and then it dies out quickly but all lights and electrics stay on. Tried jumping with a jump pack which didn’t make a slight difference but apparently they got the car started once by jumping it with another car but it wouldn’t start again after disconnecting it and then trying to start it without the jump. The battery looks to be an 80ah AGM, we tried fitting a 70ah lead acid to see if it would get it started but the car then had no power at all but had power again when we switched the batteries back? My only guess is because it needs registering and coding first but I A. Thought the interior lights would atleast come on B. Wasn’t sure we could even register it with seemingly no power? Anyway after switching the batteries back to the old one I checked for error codes and it was returning 2DEC and 2ACC - any help or suggestions would be really appreciated. I find it very confusing that the old battery can power the electrics and can light up the dash but the brand new one cant?

[BMWCCA1]

I hate to say it but you're doing something wrong. A new CORRECT battery won't really care if it is registered or not and should still start the car. You may have a completely different issue but at least get the correct battery and connect it properly. Have you even measured the voltage on the "old" battery?

[ShocknAwe]

Coding the battery is for recharging the specified Ah. It would start just fine on a known good battery.

Inspect the terminal leads and grounds.