I had a new battery fitted 8 weeks ago (due to diagnosis of a dead cell in Varta battery)
On Tuesday morning not enough power to start.
Jump start then taken to garage. 14.2 charging showing. Possible issue with battery identified. Asked by garage to use car for a couple of days and return for a further check.
No further issues with starting for two days.
Check today - meter indicating suspected dead cell in battery BUT charging rate fluctuating erratically between 11.2 and 14.8 when under load.
Does this indicate the alternator is on the way out?

No warning lights on dashboard.

Thanks for any help.....

Could well be our old friend the engine to chassis earth strap. These are notorious for failing and giving false/erratic readings as they start to break down. Get that checked first, if only to make sure yours is ok as sooner or later it WILL cause a problem.

Thank you Sam. Can you tell me where the earth strap is located please?

Having just replaced my alternator and as I have the scars on my hands and arms to prove it, I hope you don’t have the same issue as me. Mine had developed the classic noise / whine of an alternator which was ready to shuffle off this mortal coil. Can you hear anything similar? 2017 Jaguar F Pace 25t Portfolio - still part of the JLR family 😀
2009 3.6 V8 (MY2010) - my first ever diesel! - now also gone
2004 4.4 V8 Petrol Vogue - now gone

Hi chris_read, no whining from alternator......

Battery connections very much worth checking , but sounds like an alternator to me.

The 2007's were notorious for having a chocolate alternator - maybe yours was part of the same batch

KG, earth strap is mounted low down on the o/s of the engine, toward the front adjacent to the alternator itself. Could well be the alternator, but as you have to get in there anyway do make sure the strap is sound and tight.
When the battery is fully charged, how well does the engine turn over on the starter? With a fully charged battery with a decent earth the engine should spin over very quickly, so if it’s at all sluggish.....

Thanks again Sam, engine spins over quickly and starts immediately (it was -4 degrees here this morning and it started with ease).....I’ll get the earth strap checked....

Ok in that case the earth is probably good. Worth checking though if you end up having to replace the alternator.

Had battery checked again by different garage. Battery showing as being ok but in need of charging. Alternator output showed as 12.75 under load. This morning when I started it (without any problems) I got ENGINE SYSTEM FAULT for a few seconds. Engine running fine with no loss of power. Restarted a few times after a short run with no message appearing. Parked it outside for 7 hours (-2 degrees here) same message on start up, switched off then back on, same message....drove for a few miles and restarted a few times with no message appearing....I’m assuming this is related to the low battery....is that a reasonable assumption?

It has been bitterly cold and batteries don't like the cold. Went to mine yesterday to find it was below 12v, no load. Recharged to 14+ using this nifty wee charger/maintainer https://www.ringautomotive.com/en/product/RSC806

I think I may upgrade to fullfat AGM in the near future? This is about the best value I could find. https://www.tayna.co.uk/car-batteries/exide/ek950/

Good luck and keep us posted.

After reading quite a few posts on here about flat batteries I bought a NOCO jump starter from Halfords. Yet to test it.
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Thanks for all comments. It’s started without issue, with the exception of Tuesday morning. I’m going to get an auto electrician to check everything over. Don’t want to replace components when not necessary! Didn’t get the ENGINE SYSTEM FAULT message at any point today. I’ll report back......

I've just put a new alternator in my 2006 TD6 with 140,000 miles. I had several weeks of spurious warnings and occasional reluctant starts, then got the faintest flicker of the red light which I thought coincided with driving through puddles so dismissed it initially. No grinding noise, but then the red light came on and stayed on - and every warning imaginable came up as the power drained - just got home as it died! The brushes had completely worn down and the commutator had deep (4mm+) grooves! Hope you get a diagnosis - good luck.

Garage charged battery fully today then tested it again...it failed the test! Replacement (under warranty) battery being fitted on Wednesday morning.....hopefully this will resolve the issue!