Battery not keeping a charge?

[Kellu]

So I'm buying a 1993 318is and I drove it for the second time last night with the intent on buying it. The guy said that it started not holding a charge for more than a day and thinks it's the alternator. Yet when I drove it it stayed charged fine when I was driving and didn't die out at stops ect. So the alternator must be recharging it fine, and the part is only a year old. When I started it it fired up fine but when I put it in reverse and was trying to ease it out of it's tight spot the rpms suddnly dropped and it sounded like it was dying. So I put it in neutral and revved it a few times and it went back to a normal idle and stayed there the rest of the night. When I looked in the Bentley manual and it said that these are the possible problems.

A: Short circuit draining the battery.
B: Short driving trips and high electrical drain on the charging system not allowing the battery to recharge.
C: Drive belt(s) worn/damaged
D: Battery faulty
E: Battery cables loose dirty or corroded
F: Alternator or voltage regulator faulty

What do you guys think it is? Going to drive it again this morning on a cold start to see how it sounds cold, also want to take it to a shop to see what codes it will be throwing as I think there are some electrical issues(E-brake light doesn't turn off, check engine was on, and a nother light I can't remember). right now the price is down from 1200 to 1050. Would you say that's a good deal?

[Darky]

Check voltage when running ~14.4v.
Car off 12-13v

Cheers

[Kellu]

I'm guessing if it's below that when running it's the alternator?

[Darky]

I'm guessing if it's below that when running it's the alternator?

If it is below that it is definitely the alternator! But it does not eliminate it either, amps after that.
If is below the 12v without running either battery or battery has not been charged properly.
Then there's the electrolyte test.

[Nick_318is]

How old is the battery?

[Kellu]

How old is the battery?

I'm not sure, I took the alternator out since the previous owner said that was the problem since he was charging the battery and it was draining and not being recharged by the alternator. I took it to O'Reilly's to get tested to be absolutely sure and it failed on all 3 bars on the testing machine. Ordered the replacement yesterday it will be here tomorrow. Will keep you posted on how things go. I am really hoping this is the only thing that I need electrical wise to get the car running solid.

[Kellu]

  ok so I swapped the alternator and jumped the car to get it started. It ran for about 15 mins and then died out to 500rpm and started chugging then turned off. Unfortunately the gas is right on the bottom red line, I don't know how accurate the gauges on this car are. Is it possible my battery is bad? this is a brand new alternator it shouldn't be the problem now.

[Tgoode318]

Kellu Do you know how to do the stomp test for error codes? Do this and see what you get, this can help us narrow the problem. Since you have replaced the alternator though it sounds like your battery might be bad. If you look on the battery there should be a sticker with the date of the bat. If its really old it could be bad and also if the PO let the battery die and stay dead for a while that can damage even a new battery and cause it to not hold a charge. Go to a autozone or to a similar parts place and they will do a free check of your bat/alternator. By load testing your bat you will know for sure if that is your Problem. Another thing is even if you replaced your alternator with a new one you have to have your connections to the alternator torqued properly! IF it is not torqued properly and free of rust/corrosion it will not make a good connection and you will not get a charge. If you smell any kind of hot wire smell that is a good indicator it isn't torqued properly. Next is to go to your Battery Cables And make sure they are spotless! no rust/corrosion! Also Make sure the cables are well seated and torqued properly to the posts. Check all your grounds as well for corrosion.