BIG battery problem. I will pay $5 for the correct answer.

[I Like Waffle]

31.5 volts of AC

You have a bad diode or a few in the alt. Need to get that replaced, thats where your voltage is going. Problem solved, dont listen to any of these dumbasses btw. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

Also get your battery load tested while your at it. A bad alternator kills a battery, and a bad battery kills an alternator. Remember that

 

[99grandprixGT 5,000+ posts]

if its the alt pm me for me paypal. thanks.

 

[ktraughb 10+ year member]

often times when your battery light is on even when your car is running it may mean there is an alternator issue or could be as simple as a loose connection. ive seen it and its frustrating. an alternator can have issues and still charge enough while driving to maintain somewhat normal electrical operation. definitely check the connections, load test the battery, and test the alternator as well. make sure the connection from the alt to the bat is secure.

 

[I Like Waffle]

You replace your alternator yet?

 

[goingdef 10+ year member]

going by it draining in the car then rising once removed, sounds like the time I wrecked my VW it shorted something under the car no fuses would blow but it would drain the battery in minutes so I'm going with a short as for the alt light your new alt wires differently then your old one the sensor may not be hooked up try a dmm with the car off then on testing on the battery terminals if it goes up when the car is started then the alts ok it should be around 13.8v-14.6v depending on how charged the battery is to begin with and resting around 12.5v car off fully charged around 13.0v if it just came off a charger. But this is from my own experiences yours may differ just a thing to try.

 

[93dakota 10+ year member]

You need to check for parasytic electrical drains with an ammeter or you can also use a bulb to check. Could be something stuck on (heater fan, any amount of relays, etc.) that you cant notice. Possible when you got hit it jammed something in the on position, and its slowly draining the batt overnight.
A quick fix would be to put a batt disconnect switch in it when letting it sit for a while, but to find the real problem youll need to put the meter on the batt and pull fuses from the fuse boxes until the drain stops, then you know whats causing the problem and can further trace it.

Edit: One thing i forgot to mention, there could be a shorted diode in the alt, which will cause a drain. You can check this by hooking your meter up and checking for ac voltage while the car is running.

I agee with this man.