maxcollins

Hello, I'm new to the forums, not sure if this is the correct area to be posting this in so if it is not, please just move it to the correct section. Thanks

My Audi A4 battery is experiencing problems. I went away on vacation and the car was left in garage for around 40 days. It was cold around 40-60 Fahrenheit over that period. When I got back, I started the car and the lights flickered for about 3 seconds but eventually the car turned over and started. After noticing the battery was more than likely drained I kept the car started and drove it for about 45-60 minutes to try and charge it. After stopping, I went in the market for about 20 minutes and when I came out it was completely dead. Jumped it and it started right away no issues, drove it around for about 2 hours to try and keep it charged then went home and didn't touch it until the next day. Next day, it was clearly drained again and took about 3-4 seconds to start. This was yesterday, and every time I start it, it is now doing this (flickering lights for about 3-4 seconds then turning over). I've owned the car since 2016 and never once had an issue with anything. Could this be a bad battery? Or is it more likely for something to be draining it? I turn off all the lights before turning the car off, unplug everything and do an inspection to make sure nothing is on. So if something is draining the battery its not something obvious.
Any help is appreciated, wanted to search the internet before brining it in to the shop, just want to see if theres anyone else who has had this problem and was able to solve it on their own.
Thanks

SMac770

I'd run VCDS and see what the reported battery statistics are, such as voltage, state of charge, internal resistance, etc. With the ignition on but engine off, and then with the engine running to see what it jumps to with the alternator active. Could be you might need more charge/discharge activity to recover the battery state.
You can watch the current flow to/from the battery as well, though to see what you can get it down to, you'd want to turn off the climate system, MMI, the daytime running lights, close all the doors, make sure all lights are out. It'll keep reporting for up to 30 seconds after you key off the ignition, so you cannot really get a reading for with the car in its dormant state. But close.

Without VCDS (Ross-Tech), you're stuck with what you can read with a voltmeter. See what it reads with the engine off and with the engine on. Should be 12.4v/12.5v engine off if things are good. Should be 13.5v to 14.5v depending on how close the battery is to 85% state of charge (it drops the voltage as the battery reaches desired capacity).

40 days is a long time to let the car sit without disconnecting the negative or having a battery tender on it. If the battery is low on voltage, you could try letting it sit on a battery charger. Just make sure it's an AGM (I'm assuming you have an AGM battery) aware.

maxcollins

Thanks for quick reply. I'm not to great with cars but is it possible the battery still needs charge even after driving it around for 2 hours straight?

SMac770

Don't know. You don't have any numbers so it's all guessing at this point. Could be the battery is kaput from being drained to too low a voltage, could be a problem we the charging system, could be something broke and is now causing excessive drain (but I don't find that likely since the car was just sitting there; did it have battery problems before, is there any aftermarket mods that use electricity, did you leave anything in an outlet, ...).

audi8k

A problem with an aged battery and low temperatures is that the voltage increases and charging current reduces very quickly after starting. Mine is also a 2014 and I see the effect that the charging module limits the voltage to 14.9V after only 15 minutes or so with a charging current about 1A. So driving an extra hour only gives 1Ah (almost nothing)..
I got the reported capacity up from 16Ah to 40Ah by having a charger connected over the weekend. I monitor the battery state via the diagnose system (VCDS or OBD11). The interesting values are in module 19 and measuring ("Real time" values in OBD11) address 20 and 18 (with the percentage values presented in address 19).

maxcollins

Never had an issue with the car and have owned it for 4 years now. No aftermarket besides a performance chip which was installed over two years ago. I did leave a phone charger in the outlet but nothing was connected to the charger. I have since removed it.

maxcollins

Nice so it is possible my battery is just not charged enough. I live in an apartment complex and don't have access to an outlet to keep the battery plugged in while its in the car. It is a bad idea for me to remove it to charge it in my apartment?

SMac770

Might be a bit cold for outside, but I don't think I'd charge a battery in an enclosed space. At least leave a window open for ventilation. And certainly don't leave it unattended.
The problem with connecting to both the positive and the negative on the battery is with spark discharge. That's why you connect the dead side ground jumper cable not at the battery.
https://www.optimabatteries.com/en-u...ng-agm-battery
https://www.optimabatteries.com/en-u...harged-battery

You really need a voltmeter and see what your battery reads with and without the ground cable connected. You're random guessing your actions without real numbers.
Note that the repair manual technically says you should disconnect the plug on the negative cable terminal before connecting the negative cable back onto the battery. Then reconnect the plug (which is for the battery management). Guess it's out of concern for possible surging the BEM at reconnection.

maxcollins

Awesome, thank you for this.