Land Rover Repair: 1996 Discovery SE - Immobilizer Issue?, annoying habit, serpentine belt

Question
My recently acquired '96 LR Disco SE has an annoying habit of seeming to lose all power when I insert the key and turn it to start.  It isn't constant, but has been doing it pretty predictably the past couple of days.  I will eventually power up and start, but it is getting rather irritating.  The previous own had a battery maintainer installed, but I didn't get the charger portion when I got the vehicle (the owner was deceased, and his daughter didn't know anything about it).  I suspect that the battery, which tests at 11.8 volts as of this writing, is not delivering sufficient power to the system to keep the rather complex alarm system fed and happy, and this is causing the immobilizer to engage unpredictably.  Is this likely, or even possible?  The truck also loses power, seemingly at random, while driving down the highway, but then immediately powers back up with only a slight hiccup, and the radio shutting off for a moment.  Any comments would be appreciated.

Answer
Hi Patrick,

it could be the serpentine belt slipping OR the alternator is about to fail.  Both of these can cause the symptoms you describe.  I suspect the alt as this is what charges the battery but sometimes it can be the belt.  ALSO, sometimes mechanics install the belt incorrectly and this can give you some trouble.  Even LR mechanics have done this on my '95...I hope it was accidental. :(

Attach a multimeter to your alt and see how it's charging.  IF it fluctuates then you'll have to replace the alt.  Try running your AC while you monitor the alt - sometimes under load the alt (if faulting out) will reveal itself as bad.  Test the alt with both a cold and warm engine.

Best of luck,
JohnMc