I'm of the same opinion ad rrstdv8,,, 13V at idle is too low,, that will never charge a 12V battery. 12.2 or thereabouts is bordering on a discharged battery. I would expect to see 14.6 at idle and a fully charged healthy battery around 12.8 at standstill. I would be looking at the alternator first then see how the battery performs afterwards.
I also have a BM2 battery monitor fitted,, an ideal tool if you are trying to monitor the battery in real time. I was a bit dubious a to how accurate it would be but I checked it against my fluke meters and it was spot o 2010 RRS, TDV8
bali Blue / colour coded
side steps / flappy paddles
black perforated leather
22" overfinch
heated everything, TV,fridge ...... now with gold calipers and mud flaps !( black mud flaps that is) !!
Many years ago,,,,, 1955 series 1 landie , sometimes wish I had kept it

Well ive booked in for alternator this morning along with a list of stuff so it would be Ideal if those results point to alternator

Well not Ideal but simple if that makes sense

Bear in mind that a dodgy battery can kill an alternator. Be prepared to replace both but hope only the alternator is required. 2012 SDV6 - it's missing a couple of cylinders
2008 TDV8 - it was a labour of love and is much missed

Yea im prepared for that and almost tempted for sake of £150 more for new battery same time then kts warrantied

insiorc wrote:

For folks not too clued up on basic electrics then a cheap little tool can provide good info on what's going on with the battery and charging system without having to figure out a multimeter (yes a multimeter is invaluable in knowledgeable hands). It's a BM2 battery monitor which is left permanently attached to the battery which connects to your phone etc. via blutooth and stores volt data for 28 days. Even for folk familiar with a multimeter this is a handy tool (I've got 27 years experience using them for work)

Col wrote:

Dennis, does it matter which side of the BMS module the neg. terminal is connected?

It's not drawing any significant current so I don't think it matters to the car.

the monitor may get a slightly (trivial) more accurate reading connected to the battery

Dennis, I assumed the monitor connected direct to pos. and neg. battery terminals, but as on the sport the BMS bolted on the neg. terminal post just wondered if it made a difference as when hardwired a ctek plug in it was recommended the neg. terminal was connected to earth point on the vehicle not the neg. battery terminal, I realise the ctek and the monitor serve two different purposes, but just wondered if it made a difference as would not describe myself as a auto electrician. However from what you say that is how you wired the monitor in anyway.

Cheers
Col

Col, I never thought much about it, I probably would have gone directly across the battery except the -ve was tucked under the scuttle panel area so a pest to get to (probably battery out), I chose the external earth out of lazyness  13MY Range Rover Sport Autobiography SDV6 - mine
14MY Range Rover Evoque Dynamic SD4 Black Pack - wife's
99MY Defender 90 TD5, Soft Top Conversion - my toy, and bairns favourite

I'm curious as to why the engine idle volt readings seem to be the focus but not when the engine has higher rev's?

I've not had much dealings with modern so called smart charging, but if a battery is weak then can this not drag a perfectly good alternator voltage down at idle until the battery has more charge, which needs more rev's? It certainly used to be common when checking voltage that it could take a good number of seconds/minutes for the battery voltage to rise to mid 14 volts as the alternator raised the battery volts.

If I was checking my alternator I'd be letting the volts settle after starting, then with meter across the battery I'd be watching/hoping it would rise to about 14.7 ish when rev's were increased (older cars tended to be around 14.4V with rev's). Next test would be with as much load as possible, then the idle volts would likely be lower, but rise to a similar value when engine rev's increased although probably take slightly longer (and take even longer if the battery was knackered) - if this happened I'd consider the alternator likely to be good.

A rough visual indicator of a working alternator is at night with lights on and as much other load on (window heaters, seat heaters etc.) then rev the engine and the lights should get brighter.

From the readings already given, especially when rapidly dropping towards 12V when load turned on and engine idling then I'd be thinking a knackered battery. Did the engine tone change/revs drop when the load was turned on (increased load on engine hints at alternator working harder - so working). I'd suggest repeating your tests but increase engine rev's and see if the volts rise.

Maybe smart charging works different? 13MY Range Rover Sport Autobiography SDV6 - mine
14MY Range Rover Evoque Dynamic SD4 Black Pack - wife's
99MY Defender 90 TD5, Soft Top Conversion - my toy, and bairns favourite

Under load it counted down none stop from 13 to 11.9 before i turned it off so it didn't drop too low to cause more damage. As you said I put on high beam and heater to create load and it was losing voltage as fast as counting down would be

A good battery should have held that load for a while before dropping to that level, especially if not long since being charged. But it's quite common for a knackered battery to take out the alternator aswell. 13MY Range Rover Sport Autobiography SDV6 - mine
14MY Range Rover Evoque Dynamic SD4 Black Pack - wife's
99MY Defender 90 TD5, Soft Top Conversion - my toy, and bairns favourite

Well alternator is booked in so will get a battery myself and leave it in passenger footwell and say once the alternator is fitted change battery

Cant hurt I suppose to refresh