New Battery within the last 6 months
New Alternator from Auto Zone within the last 2 months (yeah I know, I learned auto zone alternators suck after buying this one)

First issue: Was getting the flashing M & S due to battery voltage being high enough to start, but low enough to cause fault.

Checked all cables and grounds. Tightened all connections, etc. Charged battery for a while so I could drive it to Auto Zone to have the battery and alternator tested without driving in limp mode. Fault went away, both components "passed" the testing at Auto Zone. Drove it the rest of the weekend without any issues.

Second issue: Last time the Rover was driven would have been sometime on Monday. Started and drove fine. May have turned over a tad slow a time or two but ran without any faults. Go to start this morning, Rover is dead in the drive way.

So its either the battery or alternator (I've read things on here about Auto Zone alternators not lasting long, of course, after I bought one) or I have some kind of electrical drain issue going on. Before the complete failure to start:

V Batt off: 12.3 V
V Batt @ idle: 14.5 V

My gut is saying the alternator is shot already, but it doesn't make sense that I'm getting that high of a voltage running at idle. I need a little direction here. It came with a "lifetime warranty" (reminds me of the Tommy Boy movie about taking a sh** in a box and marking it guaranteed) and I'm wondering that if it "passes" their test if they will give me hell about a return. Where is the best place to get an alternator for our Discos?

None the less I think what I really want to do is replace both the battery and the alternator (with a reputable one) all at the same time, as this is the 2nd or 3rd time this battery has been drained to almost nothing. I'm guessing there is no real way to test for a drain issue other than just process of elimination

 

have you tried checking to see if you have a short in the truck by putting a test light between the battery cable end and the battery post? and see if it lights.

 

Have someone do a load test on the battery with the engine off. Your alternator is putting out enough voltage but your battery may be weak.