Batt help!!!
 

OK I have a 2004 BMW 525i and since buying the car i have had to deal with this issue, so the batt(according to a cig lighter charger with a digital volt read out on it) rarely goes higher than 13.6-8V while the car is running, im unsure if thats a sign of anything or not, but the issue i am having is that when i turn the car off if i use the inside dome lights, leave door/doors open for a bit too long, or anything else that would pull a lil power from batt like listing to radio, running fan/heater for anymore than 10mins if even that long without starting it for a few mins the batt will not completely die but will no have enough power to start the car. There hasnt been any codes or anything else pointing to the cause of the issue, from the lil i know and can tell the altenator is working fine its just that the batt will not hold a charge for very long if the car is drawing from it, however if i only arm/disarm the alarm and quickly open/close doors the batt will be fine for a day or two at least enought to start the car. I am not sure how old the batt is or anything else about it but im wondering what other people think about this issue along with any ideas on what i should try doing to fix the issue, i was thinking about going to buy a batt but just wanted to make sure that wont be a waste of $$ because it was fine. o also the last time i had it checked at autozone or some similar store for free they tp;d me the batt was fine however it didnt look like the guy checking it really knew too much about ehst he was doing lol.

Anyone got any ideas?

You're at minimum charging voltage, and that's with no load on I assume. Check the voltage (at the battery) with the high beams, rear window heater, and full fan while running. If it's under 13.6 check the alternator B+. If it's still under there's a problem that requires diagnostic but likely needs an alternator. Also get the battery checked out again properly.

My opinion, if its even at 13.6-8 at the alternator post I would just get a new alternator and not risk getting stranded. Spec for good charging is typically 13.6 but that's bare min, you want over 14.

Seen many posts where the user states that they have taken their battery to Autozone, etc, where they were told that the battery was still good. Got a new battery, and all problems went away. There should be a date stamp on the top of the battery. That would be the first thing I would check.

I have also taken a batt to autozone only to have them tell me it was fine yet when I changed batt the majority of the issues I was having went away

It could be the infamous IBS (Intelligent Battery Sensor). My battery would not hold a charge for many years. Brand new batteries did the same thing. It would be better for a couple months only. Lots of people suggested the car is not going to sleep and a billion other things. Finally I ended up replacing the IBS and all was well. I was only able to listen to the radio for a whooping 10 minutes. I don't have to deal with that nonsense anymore.