Hello, there are a couple of issues. Most BMW charging system went to what is called an intelligent battery system in 2004, what that means is that the alternator charges the battery as needed, it depends on a few things, but mainly battery temperature and state of charge. As the battery gets older, it will try to charge it at a higher rate. When the battery is replaced, the battery has to be “registered” in the computer for the charging system, otherwise it will overcharge the new battery thinking it is the old one and that will kill the new battery in about 8 months or so. AAA does not have the equipment to perform this procedure as you need a scan tool with BMW software. Going by the information given, the new battery is likely dead.

The second issue is the fact that the vehicle sits for a long period. Any time a late model vehicle, that includes most manufacturers, not only a BMW issue, is not driven at least once a week the battery will have to have a trickle charger connected to it. BMW sells one or you can buy a reputable brand charger, make sure that it is on the battery and charging. The important thing to remember here is that a trickle charger is meant to keep that battery charged but not charge a dead battery. Another note, try not to jump-start the battery if at all possible. Late-model cars do not like to jump-started, the power surge can cause a lot of issues, we have had to replace computers on late model European vehicles that have been jumped.

Another possibility is that there is an issue with the charging system, this possibility will have to be diagnosed by a reputable shop with the proper equipment. Please let me know if there is anything else I can help you with.

Gil Neves