Is it my alternator?

I drive a '98 VW Golf, and it’s in pretty good shape for a car its age. However, whenever the temperature gets below freezing (I live in Minnesota, so this happens regularly), my battery will die within 2 days if I don’t drive the car. The first two times that this happened, I went in and replaced the battery. The first battery was old, so this wasn’t unexpected, and I assumed that the second battery was defective. Now that it’s happened to a third battery, I’m leaning away from battery problems.

My initial instinct is that I need to replace the alternator. However, the alternator seems to recharge the battery once I jump start the car and take it out for a long drive across the frozen tundra, so this tells me that the alternator is at least partially functional. The car has 120k+ on it, and it is still the original alternator, but I really don’t want to spend an hour standing in a frozen parking lot replacing an expensive alternator if that isn’t the problem. What do you all in the Car Talk Community think? Do you vote alternator, or is there something else that you think I should look into. Any half-way knowledgeable opinion is greatly appreciated.

Well if it DOESN’T happen if you don’t drive for 2 days…then it’s NOT the Alternator. If you drive the car every day and the battery still starts the car…then it’s NOT the alternator. Something is draining the battery.

This may be difficult to find…Aftermarket security system, or sound system…Dome light on…

Have a qualified mechanic check the alternator for AC current and volt/amp output. If it passes the tests disconnect the battery negative cable whenever parked for more than a few hours. If the battery holds a charge with the cable off there is a phantom discharge in the system. Post back results for further advice. There are several here with a great deal of experience with such problems.

“the alternator seems to recharge the battery once I jump start the car and take it out for a long drive”

Be wary of this assumption. Without actually checking the battery’s voltage, you really don;t know if it’s being fully charged. Once you warm up the engine, it’ll take a lot less oomph to start it again, and this could mislead you into thinking the battery has been fully charged.

The bottom line is that you need to start by

  1. having the battery and charging system checked and
  2. having the system checked for parasitic drain.

Meanwhile, be sure your trunk light is off.

Oh, and by the way, do you plug in an engine heater at night? When I lived in North Dakota it used to get so cold at night that without one it was often impossible to start the engine in the morning. Well below zero ambient temps can do that.

All the advice so far is on point…I’d like to add how CRITICAL the battery connections are …in any vehicle… Make sure all your batt connections are cleaned and conditioned (grease or batt spray)…ALSO trace where your negative batt cable goes…make sure both ends are CLEAN AND TIGHT… In fact tighten ALL the grounds you find…IN VW’s they are STILL brown in color I believe.

Also V-Dubs are notorious for having weird radio wiring…I.e. The radio will work with the car and key OFF…Not sure when they corrected this but it used to be true on ALL VW’s and even up to the 90’s as well.

SO clean and tighten and condition ALL batt connections…AND GROUNDS… Do you have an aftermarket radio in this VW? Because if you do and the person who installed it was not familiar with V-Dubs chances are high that they screwed it up.