Battery: Should I stop worrying

[Paulhs]

Car is my partners 2017 A3 1.0 SE bought May 2019 and 3 years old on 31/01/20

At the end of December, the battery appeared (to me) to be struggling to turn the engine over. Not really struggling, just not what you'd expect of a 1.0 engine with a 700CCA EFB battery. We're talking maybe 3 secs to start the car (whereas my old Clio starts instantly). So I started checking the battery. She has had Stop/Start turned off since going back to work on 02/01/20.

I have lots of readings taken with a basic multimeter. Basically (with Stop/Start turned off manually each morning) by 17/01/20 the reading had recovered from a low of 12.12v on 31/12/19 to 12.59. By 19/01/20 left standing it had dropped to 12.25v.

By 23/01/20 it had recovered to (best ever) 12.64v and today, with no use since 24/01/20 it has dropped to 12.35.

Are these drops in voltage just normal due to the electrical equipment (e.g. immobiliser) continuing to draw power when the engine is switched off?

Just to add, I did take it to Halfords for a battery check over a week ago. His tester said the battery was Good but could do with a long run to charge it up. Daily mileage is about 22 miles. We don't have access to connect a charger overnight, so would have to disconnect and bring into the house.

 

[RichardT]

If it always starts you may be being too analytical.
You say it takes 3 secs to start. Does it turn the engine over OK during that time? Could be something else causing it to not start even when it’s turned over.
How does stop/start perform? Once the car is going does that restart it quickly?

 

[NHN]

Seems fine to me, I'd put on a ctek 8 stage charger, see how that goes, but it's lowest is above 12v so it should be fine.

 

[Wibbly]

A side effect of the 3 secs is that you may get a bit more oil pressure built up quicker, which would not be a bad thing. ;-)

 

[mikemod]

Mine is Aug 2016 and I've just had to replace the battery so may be on it's way out.

Mine was getting slow to turn over but still started.
Last year I had to leave the car for six weeks, it started OK, went for a ten mile drive but when I tried to start it again the battery was flat.
Tried charging it but it wouldn't hold the charge for long.

I never had any low battery warnings come up on the dash strangely enough apart from once when I was sitting stopped with the radio on.

 

[Wibbly]

Batteries can give wierd behavious once they begin to die. I had one car that would seem to start on full battery power one day, and fail to turn over the engine enough another. Always shortish trips but charging manually didn't help. I put it down to "shrapnel" washing around in the bottom of the battery which affected it depending on how it had sloshed around the previous time I drove it, but who knows. New battery fixed it.

 

[Paulhs]

If it always starts you may be being too analytical.
You say it takes 3 secs to start. Does it turn the engine over OK during that time? Could be something else causing it to not start even when it’s turned over.
How does stop/start perform? Once the car is going does that restart it quickly?

Yes it turns the engine ok. No, I don't think anything else is causing it not to start instantly; it starts fine once warm. Also, if you read my post, I only said it took maybe 3 secs when I tried to start it at the end of Dec when the multimeter reading was 12.12v, not always.

Stop-start performed ok when we were using it and yes it re-started the car quickly (the electronics would have de-activated the stop-start if they didn't think it had enough battery power to operate).

Any auto-electricians on here that can tell me if a drop of 0.29v in 4 days without starting the car is just normal drain?