Hi Fellow Members,

So this is my first post and thanks for all the knowledge that you all share here.

I am having trouble with a 2010 S80 3.2 I6 that I bought from private party, unfortunately I did not take the car through inspection before buying. Car was very seldom driven by previous owner and last tune up (oil change, spark plug change, etc) was an year ago, since then car has been driven only 1.5k Mike's, for a total odometer reading of close to 21.5 k in 10.5 years.

Issue details:- from very first day of my ownership, car was misfiring with cold start, felt like a low battery issue to me, but as soon as the car started I got check engine light on continuously, drove the car it runs very smooth, no issues while rubbing, no rough idle either.

Now this issue happened for 3 days continuously, only happening while cold start in chilly Denver mornings this month, no issue after that first start. I got the obd codes checked and got P0300 for random misfire and few cylinder specific misfire codes like P0301, P0302, etc for I think 5 out of 6 cylinders.

Fix done:-- Opened the hood, listened and could hear some whining sound from battery compartment after the car engine was stopped, post first drive of the day. Thought bad battery was causing the starting terrible and may be misfires also due to insufficient voltage for ignition coils or fuel pump etc and had the battery replaced yesterday. Now as I removed battery the CEL light went away, car passed state Emission test and well right after and everything was good.

Next morning when I started the car (with new battery) it again misfired and then a new message came up on dashboard " Try to slow down or shift up" with CEL flashing, put car in reverse and it started shuddering heavily, but as soon as I reversed out of parking space and put transmission in Drive, suddenly the CEL and message on dashboard went away, car drove perfectly fine again. After driving for a mile or so, shut down the engine and checked under the hood, was able to hear same whining sound from battery compartment. Did not pull any codes afterwards yet.

Now I have no clue what's happening----

1. Why s brand new battery is making this whining sound ? (Attached video)

2 what might be catching these new shuddering symptom and flashing CEL ?

3. Engine is still misfiring at cold start, why ?

So I never have faced any issue while driving during the day or starting the car later in the day with misfires or anything else, except few misfires on older battery, when I trying out to start and stop the engine multiple times in few mins.

Apologies for the long post, but please really need your help and feedback, I am lost here. Do not want to talk it to a mechanic and have blind faith on him.

Thanks

Newbie