In the past couple of months I have replaced a battery that didn't seem to be holding charge and thought I had recovered the battery, which I found depleted to 5.4 V. Everything has been hunky-dory until the electrics took a bit of a hammering on Saturday: off-road, heated-seats, headlights, LED lightbar, heating, various chargers all going. Toward the end of the day the red 'battery' lamp illuminated; I assumed this was because more was being taken out of the battery than the alternator was able to supply and didn't worry too much. The only 'voltmeter' I had was a bluetooth module for playing music on the radio. This showed 11.4 V, going up to 12.1 V when the engine was started - not accurate, but indicative.

The next day, the car started fine and the red battery lamp illuminated. After another couple of miles, all hell broke loose: Gearbox fault... Suspension Fault... No HDC No Terrain Response, etc., with the speedo / revcounter / fuel / temp gauges doing their impression of windscreen wipers. The battery connections were fine and all fuses seemed OK. The OBD parameter "Voltage at Control Module" showed a voltage following various exponential curves as engine speed changed, up to approx 17 V, down to approx 14 V. I took a chance that the things would sort themselves out when the battery voltage got back to 'normal' and the regulator (or LR equivalent) would start working again. This seemed to pay off and after another half an hour everything went back to normal (not even the battery lamp showed). With a working assumption that I could be coasting to a halt at any moment, heralded only by the suspension dropping, we headed home.

Halfway home, that OBD parameter dropped to zero and the red lamp re-illuminated. The voltage received by the OBD reader itself was at 11.9 V and gradually reduced. Two miles from home, the dashcam switched-off with a 'low voltage' warning.

Still starts and runs but with red battery light illuminated. I'm now 100 miles away from the car for the week and can't get my wife to start prodding around with a multi-meter. My chief suspect (to order so as to be ready when I get home on Saturday) is the alternator, but am I overlooking some strange LR-specific module/system/EPCU? Someone mentioned a 'power management' function that controlled such things (including load-shedding).

Cheers,

Hugh

Genuinely no expert here but in short it sounds very much like you have no power - that rather rules out the power manageent system in my book 2012 SDV6 HSE (technically its hers)
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Are you sure your battery recovered properly?

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I would get the battery checked by a battery expert. I have never managed to recover a battery that has been down so far as yours. I have charged them and think they are OK and then they fail when put under load. 2023 P440e SE Dynamic on order -cancelled

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As above, dodgy battery? A faulty battery is a fairly reliable way to take out an alternator, and we say 0.8V per cell can be 'the point of no recovery', so your 5.4V is under the 9.6V minimum (assuming standard wet cell). Your battery paperwork will have a recommended charge rate which will be in the region of 10%, so charging at anything less wouldn't help, regardless of what it says on the fancy charger box (thinking 5A CTek etc.). Personally, knowing the cost of Landrover parts I'd have played safe and repurposed that battery. Good luck 13MY Range Rover Sport Autobiography SDV6 - mine
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It might be prudent to change battery and alternator then. The 'old' battery can run an inverter. In fact, if I connect the charger to the inverter, I'll have unlimited free energy!

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I would order a denso alternator
and reasonably priced battery.


If ever you see 16 or 17v again, you need to keep the engine revs down, until you get home

If you were seeing 17V out of the alternator (and voltage rising with engine speed) then the regulator is goosed. You might be able to get a regulator pack separately to the alternator (I did on my old 645 - £50 regulator vs. £600 alternator!) but given the cost of a Denso alternator I'd be tempted just to change the lot; better that than doing the regulator now and finding the brushes or bearings give up in six months time.

So yeah - best to ask Santa for a new battery and alternator!  2014 BMW 530d Touring, 2006 BMW 650i, 2018 Mini Cooper S