Hi Gibbo.....Murphys Law states that the strap over the battery has to hide the date!! If any help, the car was new in July 14 so battery can't be more than 4 years old. It's a big old boy as the car is a 320D with stop/start (that I have programmed out never to darken my door again!!)
The car will start perfectly and then next time it sounds like the battery is flat and it only just turns over but always starts. Sometimes it does it a few times and then not for ten or more starts...it's done this since I bought it 18 months ago and has never failed to actually start but sounds dreadful sometimes. A few people passing have said 'only just eh!!'
If you imagine you've left your lights on for a few hours..that's what it sounds like.......sometimes happens straight after a 200 mile run!
I suspected the battery strap as this is a common problem with the F30 apparently but it was fine when Dilly looked at it yesterday....suspects now are lazy starter or possibly the battery...charging circuit seems fine.