R57 - alternator / charging woes

[thekingisdead]

2013 R57 Cooper S

- alternator stopped charging on me last week, confirmed with no increase in battery voltage whilst engine running so I swapped out for a new alternator.

- Cue celebration (this is the largest DIY job I've undertaken) when the battery records ~13.9v whilst running on the new alternator.

- I use the car for ~2.5hrs, including 1hr 15 at freeway speeds with AC and stereo running etc. So the alternator was charging with no problem.

-Towards the end of the journey I get a 'battery low charge' warning - thankfully I made it home.

I've checked the battery voltage again this morning and it's now showing no charge whilst running. I've checked the belt is in place and the electrical connector is secure.

Any ideas where I should look next?

the battery is under 6 months old.

[E-bmw]

thekingisdead said:

2013 R57 Cooper S

- alternator stopped charging on me last week, confirmed with no increase in battery voltage whilst engine running so I swapped out for a new alternator.

- Cue celebration (this is the largest DIY job I've undertaken) when the battery records ~13.9v whilst running on the new alternator.

- I use the car for ~2.5hrs, including 1hr 15 at freeway speeds with AC and stereo running etc. So the alternator was charging with no problem.

-Towards the end of the journey I get a 'battery low charge' warning - thankfully I made it home.

I've checked the battery voltage again this morning and it's now showing no charge whilst running. I've checked the belt is in place and the electrical connector is secure.

the battery is under 6 months old.

It will likely either be duff alternator or duff battery.

Either could be true regardless of the age of them.

If the battery wasn't very good due to the failing alternator it could easily have been severely weakened up to that point.

You say it is showing "no charge" but don't say how you come to this conclusion.

You also say you were out for 2.5 hours..........so the battery was charging with no problem, but it is actually not possible to say that from what you are saying.

13.9 volts from an alternator into a low battery isn't as high as I would be expecting, at what engine revs was that?

If it were mine I would be borrowing someone's known good battery & doing a non-running/running comparison to see what voltage the alternator is putting out under high load (full lights, air con, etc all on) conditions.

If I were a gambling man based on the info you have given in your first post I would be thinking most likely the battery, but you still need to do more as above to be certain.