Hi, I posted this in a different sub-forum yesterday but it was suggested I may get better help here.

My daughter has a 72 plate Kodiaq which this morning had a random flat battery for no obvious reason.

When it was last serviced 2 months ago by our excellent independent VW/Audi specialist (who have looked after various cars in our family over the last 10 years) they indicated the battery was starting to fail.

We jump started it and she's been using it without problems all day (the engine management light which had been triggered went off as well).

She booked it into to Halfords this afternoon for a battery replacement and they strangely found the battery to be in good health but found a high Diode Ripple reading of 1.21V. They did not consider the battery needed replacing but suggested a further diagnostic check.

I'd not heard of diode ripple before but looking it up online suggests it's a warning of impending alternator failure. This seems very strange in a car with 23k miles only and otherwise running perfectly. Annoyingly the car is a couple of months out of warranty.

Does anyone have any experience of this issue or advice please.

Many thanks.

Good morning John, welcome to the forum.

Very unlikely that your battery will be testing as 'good' if it wasn't fully recharged after being discharged - so I'd treat halfrauds test with caution, but admittedly strange that they wouldn't want to sell you a new battery!

It is possible that a diode in the bridge rectifier has failed - this could cause the battery to discharge while standing - I'd suggest having the alternator fully tested to rule out any fault there.