nthreasher

hi all, I've been chasing a battery discharge issue for a long time... In winter it'll lose charge overnight

Should there be a voltage delta between posts and battery itself?
Battery out i measured 12.14 (battery tested at 900CCA, so I'm told it was ok)
Put it in the car and measured 11.93 under the hood
Could there be a ground issue on main battery feed?

Alternator is a few years old, and pulled every fuse and ruled out parasitic draw

Voltage regulator maybe? It's a 2009 avant

nthreasher

Also, running it measured 12.96 under the hood. Positive post and negative post, as well as negative to alternator, both the same

Once I jump it, runs with no issues until it sits again and loses charge...

dreadlocks

un your battery has a dead cell and thats the parasitic draw if its fully charged at 12.1v, should be closer to 12.9v idle at rest, ~14v charging.
solution: get a new battery, whoever tested it good didnt know what they were doing.

nthreasher

Thanks, battery was low when it was tested at advance auto. Idle varies but I've measured 12.96v

It's drained so many times it can't be in the best shape... But I don't want to keep replacing batteries if I'm losing to a draw elsewhere ... Battery is 2-3 years old, duralast platinum iif i remember

nthreasher

Think I misunderstood your post, should be 12.9 off and 14 engine idling?

dreadlocks

sorry I used the word idle incorrectly, too much baggage.. A good battery should be doing ~12.9-13.2v with no loads and with no charge (engine off), in a resting state..

3 years for a battery is pretty typical depending on your climate and driving habits.. sometimes I can get 4 out of em.

If a battery has an internal failure like this they will self discharge rapidly, as soon as you take it off a charger they start shedding volts til they are flat again.. but for a while they are still capable of starting a vehicle, so the monkey at advanced auto would be able to pull enough amps to start it no problem if he ignored the glaring voltage issues.. you coulda turned the key and figured that out.

The people at your local Advanced Auto are not trained to operate any tools, including the one between their ears.

SMac770

My 2009 avant has a type 49 AGM battery under the spare tire. It's 10 years old.
If I remove the spare and measure between the posts of the installed battery, I read 12.42v.
If I open the hood and read between the positive post under the plenum cover and the alternator housing, I read 12.42v.
These are with the ignition and engine off.
VCDS reports my state of charge as 85% (normal, seems Audi doesn't try and push the charging of the battery back to 100% SOC) and load aging around 55%.

12.1v on an unloaded battery is nearly no state of charge (SOC).
Take it out of the car and put it on a charger and see if it can get back to 12.7v (the starting point for 100% SOC).

You may or may not have the tool for it, but I'd put an ammeter between the battery negative post and the cable that would go on the negative post and see how much current draw you have. Same for with the ignition on. BUT DO NOT try to crank the car with an ammeter inline.
It could be you have an excessive draw by a component that's only on when the engine is running, or maybe your alternator is simply not producing enough recharge, if the battery was able to charge up isolated from the car.

jagtoes

At 12.4 v no load the battery is failing. There are 6 cells in the battery with each cell measuring 2.1 volts thus a fully charged battery should be 12.6 Volts. If you get 10 years on a battery you are lucky with todays cars drain on the electrical system. Voltage at idle should be between 13.8 to 14.4 and depending on what type of charging system you have it will vary. AGM batteries charge differently then flood type batteries so when you charge it make sure your charger can charge AGM type .

dreadlocks

its actually 2.2v per cell, so 13.2v is a fully charged new battery..

SMac lives in Georgia, people in the southern states can get batteries to last alot longer than those of us with actual winters.. aint nobody getting 10 years out of a battery here in Colorado..

kentr

FWIW I'm WAY over my pay grade on this subject but did find this chart at: https://carbatteryworld.com/car-battery-voltage/ (see info from Optima Batteries below chart) Interestingly enough, my dealer checked my battery and it checked out at 12.3 volts according to them. The work order further stated, "Audi min. spec is 11.5 volts. No repairs needed at this time." According to the referenced site, 11.5 volts puts in on the edge of almost complete failure. Hmmmmm



In part from Optima at: https://www.optimabatteries.com/en-u...mber-batteries