Low battery warning not fixed with new battery
 

Hi All

Grateful for some urgent thoughts on this one. Came to start my car (4.2 TDI) and got a “Low battery, battery will charge while driving” message (or something similar), completely out of the blue. This was accompanied by a slew of error messages about all sorts of systems, I guess due to the low power. Luckily my car was at my Audi indie for other stuff so they kept in and did some tests and could see that the battery wasn’t receiving much charge. They replaced the battery which appeared at first to have cured the problem but on testing today the problem is back. Although the alternator is one possibility it’s apparently not a foregone conclusion as it gets a signal from the CAN bus to activate and it could be something to do with that. Replacing the alternator is an 11 hour job so not something they want to do speculatively. The whole thing is proving a bit of a head scratcher, so if anyone has any thoughts I’d be very grateful.

Cheers - Graham

was the replacement battery to the same spec as the original? And was it charged prior to fitting? I've often found new batteries are only about half charged when supplied, so if the fact the battery loses charge is down to periods of inactivity, short runs, heavy electrical load, it can quickly pull a new battery down to the same state.

I'm assuming it's been coded by the supplying garage, so it's recognising the battery as 'new'.

I'd probably suggest connecting a decent quality battery charger to it and see how long it takes to get it up to fully charged. Mine is by no means top end in battery charger terms (mine's a Ring one bought from Halfords)

https://www.halfords.com/workshop-to...e-and-diagnose

If the car sits for periods not being used, it also has a maintenance mode which will top up at 0.8A as and when required.

Many thanks for the quick reply Adrian! The car is still with my garage so I don't know exactly the state of the battery but I'm pretty sure it will have been of the same spec and has definitely been coded (it's an Audi independent garage). I can't remember the exact details but through what they are seeing through VCDS I think they have been able to rule out the battery as the problem. I will check though!

Quick update on this. Long story short turns out the problem was the alternator, which once my garage got to it was visibly damaged, as was the wiring harness (looks like high current had melted the insulation). Currently waiting for parts to arrive from Germany. Pretty big job to fix this - £2k+ for alternator and wiring harness and labour, luckily some of it is covered by a warranty. On the plus side I've got a brand new battery fitted so that job's sorted :ROFL:.

Glad it's getting sorted - if it's any consolation, just changing the thermostat housing and water pump on my Mk7 Golf GTI takes 4 hours :-( that needed doing after 4 years/30k miles......

Thanks Adrian! Have just got car back and everything sorted. Total cost just under £3k, but that was including new alternator (these are water cooled I was surprised to learn), gaskets and other stuff for the RHS turbo which has to be removed, new wiring harness, new battery (properly coded) and the cost of round-tripping the car to an Audi dealer for an independent diagnosis. And also about 16 hours of labour. My garage (AM Cars) have just been amazing at getting this sorted for me.

Weirdly, some stuff that wasn't working before has now sprung in to life, such as the rear sunshade and cornering lights. The previous battery hadn't been coded properly - can this cause weird issues with the electrics?

100% yes +++

Glad it is sorted!