2.8QS Battery Issues
 

I'm hoping for some assistance with a battery issue on the A8 (actually belongs to my Mum) Apologies in advance for War and Peace but trying to get all the relevant info in.
Car wouldn't start on Sunday night so I put the battery on charge for a few hours (to let me Mum travel home) and tried it again. Car started fine and I put the meter across the terminals when the engine was running and lights were on and it read 14.0V.
(I didn't have heateed rear screen etc on, just the lights)
I decided to charge the battery properly once she was home, so followed her home and charged it on the bench.
The battery reading was 12.61V fully charged. After 24 hours on the kitchen floor with nothing connected, the reading had dropped to 12.25V.
I thought this looked like the battery and took it to Halfords as it is still under warranty (after giving another charge this afternoon to help with the test)

Halfords tested it with a Bosch BAT121 and it failed, telling me it was unserviceable and had failed due to a charging problem with the car so not guaranteed! "It is either over or under charging", said the assistant.
"I would imagine overcharging would be relevant since I'm standing in Halfords", I replied - No response........
The printout showed a test voltage of 12.38V, start capacity of 75%.
I asked if the battery should be fully charged for the test and he told me it was as it was over 12V........

Any help or advice greatly appreciated. I have VAG-COM lite for further testing.
If I have to buy a new battery then fine, it'll get my Mum back on the road. I suppose I will need to re-charge the battery and then test the alternator with a full load as well.
As an aside, my Mum is very hard on the battery as it's mainly local runs (2-3miles) and due to a bad knee, the electric seat/wheel is moved back and forward every time she gets in and out. Add on the heated rear screeen etc and I wonder if this is responsible? 2.5 years out of a Halfords 3 year warranty battery? If that's the case then fair enough.
Thanks in advance,
Grant

Loved that, made me chuckle +++

I was once told, plausibly, that the problem with buying batteries from the likes of Halfords is that you dont really know how long its been sat on the shelf.... At least if you get it changed at a garage they likely order one in from a distributor with a high turnover, thus it is likely 'new'

It is all the wrong time of year for batteries, cold weather, high demand combined with short journeys is a killer. If the car is a keeper ,I'd fork out for a new battery for it - It seems a likely culprit and you should see an instant improvement. Maybe take it to a garage who are willing to test your battery independently and give you some assurance a new one will help - I.e. if it doesnt, tell em to take it back .. +++

Short trips would leave battery constantly undercharged which could greatly reduce it's lifespan. Halfrauds should just suck it up and replace under warranty. Only thing you can do is get third party mechanic to test charging system and if it tests OK which it probably will show report to Halfrauds and ask them to replace it FOC.

Go to another Halfrauds store and ask them for a replacement

Thanks for taking the time to reply everyone. Much appreciated.
Taking all your comments on board, I realise the local running is almost certainly killing it so I'm going to give it another charge and try a different Halfords tomorrow.
If they don't replace it, I'll pick a new battery up elsewhere to get the car running again as this is the priority for me.
I'll get the charging system double checked next week when I have time by a third party and see if Halfords replace the battery with some evidence. If they do, I'll have a new battery to sell, or maybe I should buy my own A8 to put it in!
Thanks again for the advice.

Nice to hear from you again Grant. How's the old girl going (the '8, not your mum!) :)

I'd still like that photo of all 3 of my '8s one day if you get a chance. I could even wash the car for you before the photos!

This could be one of these rare events when a trip to your friendly main agent or a local garage may be prudent, I'd want to know the reason for the battery under/overcharging, and resolve any issues before renewing the battery. The problem could be as simple as a corroded earth wire;)

Hope this helps.

Paul

And mine as well Jim!!! +++ If I leave the car with you every Saturday, you could wash and then take a photo! :p

No problem. I'll get the sponge, washing up liquid and gritty chammy ready! :)

Battery Update.
I took the battery into a different Halfords yesterday and the guy tested it and said it had passed!
I asked them to keep it overnight so they tested it again today and it passed again!
The member of staff was very helpful and even tried charging it for a bit and then testing it to see if he could get a different result but it was always fine.
It's back in the car now so I'll keep an eye on it for a few weeks.

I did a quick test with the engine running across the terminals and the reading was 14.3V.
I then put on the heated rear window/lights/blower and it dropped to 14.1V and remained steady. When I put off the equipment, it rose again to 14.3V.
I was under the impression that when you put on say the rear window, the voltage might drop slightly but recover quickly in a few seconds but that is not the case here.
I'll have to get it into an auto electrician to get it properly checked but wondered if anyone had any further thoughts etc?
Thanks.

P.S. Jim, my Mum still loves the car. She drove my A6 tdi recently and asked me what was wrong with it to which I replied, "You've become an A8 snob - that's what is wrong with it"