Jeep Repair: Alternator, voltage drop test, amp meter

Question
Hi,
I have a 1994 jeep G.C. limited with a 6 cyl.
The problem I am having is with the life of the battery.  Summer time is rare but during winter the car has many a dead battery.  There are no shorts, I measure with a amp meter. Battery was 12.2 volts.
With the engine running at idle the voltage was about 13.5 and under full load (heater,lights,etc) the voltage was still ok.

This is the third battery in 3 years.  I get a new one for free at walmart (their best battery).

I measured at the alternator terminal also. it's ok

I put a charger on the battery during the cold months a fully charge the battery.  But it will die in a couple of days.  I only drive about 2 miles to work.

Any advise would help..

Thanks a lot
bob

Answer
The short drives is not your friend.  You're barely giving it enough time to warm up much less charge back up.  But, you're leaving it on the charger so I beleive the majority of the problem lies elsewhere.

First I'd like to know exactly which battery you're getting.  If it's a Never.... I mean, Everstart then they are junk.  I used to work at wal-mart years ago and can tell you even the best everstart was still junk.  I run an Optima Red top myself but that may be a bit over-kill for most.

Next I would question battery terminals.  Corrosion, cracking and any kind of build-up may prevent the battery from charging.  

Next I would want to know if you're wires from the battery to the altenator are good.  The best way to do this is a voltage drop test.  Take the meter in voltmeter mode and go from Battery positive (B+) to the big red wire on the back of the altenator.  Basically, you're providing a second path for the current to go in the event that the original path just isn't quite up to par.  If you have any voltage over say 0.3v then you may have something to worry about.

After that I would verify grounds are good.  Maybe even disconnect a few, scuff up the metal where they contact and reattatch the ground and bolt.  

Once you've done all of this I would begin to question whether or not you've got a draw at key off.  This can be something as simple as a door ajar switch going bad, an under-hood lamp staying on, a glove box light, or even one of your modules staying awake longer than it's supposed to.

Given the current season I don't know if we'll be able to reproduce your concern but if you have  test light and a multimeter then we can start checking now and hopefully have the problem fixed by winter.
Doug