Thanks for this info... checked it out earlier today and yup, radio turns on. Bad design for a voltahe sensitive truck I'd say...

 

Agreed...

 

I can't see the battery being fully discharged by the radio being left on, unless it's already pretty low.
The radio only remains on for 20 min with the ignition off and a good well charged battery will not be discharged by that. I regularly use my radio with the key out while waiting for SWMBO to finish shopping or when taking my lunch break and listening to some light music.
If your radio discharges the battery you should consider the possibility of a bad alternator (but houm-wa you tell us your's practically new) or the battery is on its way out or some other battery draining problem. I'd be inclined the test the battery and alternator to rule them out.

 

Yep on my LR3 (just had gone on a 30mile drive) it idled at like 1100RPM and a LR Master Tech of mine said the computer is trying to get the battery to charge so it increases the idle speed until it's happy with the battery voltage. Mine would idle up & then idle down constantly. That was clue #1, clue #2 was all sorts of random low voltage faults viewed thru my iCarsoft LRII Scantool, and finally clue #3 was it trying to start and as soon as the starter engaged it instantly thru HDC Fault, Transmission Fault, and emergency brake faults. Then I metered the battery and it dropped instantly from 13.9v all the way down to 10.9v. The battery was not holding a charge once the engine was off. That's a good way to toast an alternator due to overcharging.

 

It's not supposed to let you do that, though I've done it before - I had plenty of power but it just didn't want to start. Then again my starter was bad shortly after (click but no latch on solenoid).

I believe it even states in the manual, the thing knows when the battery is low and will turn everything off accordingly. Interior lights and radio have auto-off anyways.

If it didn't start after you shut it off, it could be the battery and not the alternator. The alternator was keeping the car running, not the battery - as soon as you turned it off, you lost your external power source.

Theres a few different primary batt / gnd connections you could check for corrosion - but if you just changed the alternator and you have good running charge voltage, then it could be the battery. I'd run over to advance autoparts and throw a load on it and just see.

If not, it's some other really strange fault.

 

Well...sort of a mystery then. I had the batt shop test the battery, starter and alternator and all were good. I didn't know that about the 20 minute time-out on the radio.

 

I love mysteries!..... Hope this one stretches out like this one.

Faulty relay after 12 months...

https://landroverforums.com/forum/lr...driving-52159/

Side note, relays hate power fluctuations, regardless of cause.